Here’s how to fix problems with macOS Big Sur

Big Sur is a terrific update to macOS. But, like any new operating system, it’s not without its problems. For example, Catalina caused many problems, some of them serious, for many users. Thankfully, for most of us, the problems we’re likely to run into are much less serious and usually have a straightforward fix. In this article, we’ll examine some of the most common macOS Big Sur issues and fixes.

12 macOS Big Sur issues

In this blog post, we’re covering the issues that may occur during Big Sur installation and after you've upgraded your Mac. If you’re interested in resolving a particular issue, just go through this list and choose the one that relates to you:

  1. macOS Big Sur won’t download
  2. macOS Big Sur won’t install
  3. macOS Big Sur freezing
  4. macOS Big Sur setup fails
  5. macOS Big Sur won’t boot
  6. macOS Big Sur is running slow
  7. Apps are not launching on Big Sur
  8. Bluetooth is not working on macOS Big Sur
  9. Wi-Fi problems on macOS Big Sur
  10. Battery drain on macOS Big Sur
  11. USB devices disconnecting randomly on Big Sur
  12. Grey screen with mouse pointer on Big Sur

1. macOS Big Sur won’t download

If you see a message while you’re downloading Big Sur that says, "macOS Big Sur download has failed," there could be a number of reasons. Here’s what to do when macOS Big Sur won’t download.

  1. Check your Internet connection.
  2. Check Apple’s system status page. It could be that the download server is down or is very busy, and that’s why your download failed.
  3. Make sure you have enough free space. Go to the Apple menu and choose About this Mac. Click on the Storage tab. You should have at least 16GB available in order to install Big Sur. If not, you’ll need to delete files.

Have you got enough free space?

It can be difficult to decide what files to remove and what to keep. However, there are many files on your Mac that take up several gigabytes of space that you probably don’t even realize are there. These include temporary files, cache, language support files, and many others. CleanMyMac X can identify those files and allow you to remove them with a couple of clicks, potentially clawing back gigabytes of space.

CleanMyMac X has a free version you can try, and this app is notarized by Apple. 

More ideas when macOS Big Sur won’t download

  1. Try connecting to your router with an Ethernet cable instead of by wifi if you can.
  2. Look for the unfinished download file. Check your Downloads folder and Applications folder. When you find it, drag it to the Trash, empty it, restart your Mac, and try again.

2. macOS Big Sur won’t install

If the download completes successfully, but macOS Big Sur won’t install, there are a few things you should try.

  1. Reboot your Mac in Safe Mode by holding down Shift while it boots. Then try and install Big Sur again.
  2. Reset NVRAM. Shut down your Mac. Boot it while holding Cmd + Option + P + R. Release the keys when you hear the startup chime or see the Apple logo on screen.

Also, double-check that your Mac is compatible. The list of Macs on which Big Sur is supported is below:

  • Any Mac Pro or iMac Pro
  • MacBook Pro and MacBook Air 2013 and later
  • iMac and Mac mini 2014 and later
  • MacBook 2015 and later

If you see the "Installation failed: an error occurred while installing the selected updates" message, the first thing you should do is restart your Mac. If this doesn't help, the problem is probably on Apple's side. Wait for some time, and try installing the macOS Big Sur again.

3. macOS Big Sur freezing

Your Mac freezes after the upgrade? Your apps and programs can actually be the reason why macOS Big Sur is freezing. 

To quit the unresponsive app, press Command-Option-Esc. This will initiate a Force Quit menu. Click the app that makes your macOS freeze (it will usually have not responding status) and press Force Quit.

If the problem persists, running CleanMyMac X can help fix performance issues, including freezing. Here’s how you can quickly get your Mac back to normal: 

  1. Download CleanMyMac X (a free trial is available). 
  2. Install and launch the app. Go to the Maintenance feature. 
  3. Check the boxes next to the processes you want to run (we recommend selecting the first four fixes and Repair Disk Permissions). 
  4. Press Run.

CleanMyMac X is not a magic pill for all Mac problems, but it does fix things sometimes. It’s especially useful when you have a lot of conflicting software and want to clear up things a bit.

4. macOS Big Sur setup fails

This error occurs after your Mac has updated to Big Sur, but during the setup process. Here’s what to do when macOS Big Sur setup fails:

  1. Hold down the Power button to force your Mac to shut down.
  2. Press the power button again to start it up. It should now boot into Big Sur.

5. macOS Big Sur won’t boot

If you’ve successfully installed macOS Big Sur, congratulations! You’ve cleared the biggest hurdle. However, you may still run into problems, one of which might be that Big Sur fails to boot. Here’s a checklist to follow if macOS Big Sur won’t boot.

  • Check the power supply — this may sound ridiculously simple, but that’s why it’s at the top of the list. If you’re using a laptop, plug it into its charger. If it’s already plugged in, make sure the connection is secure at the wall and on your Mac. If you’re using a desktop Mac, make sure the power cable is secure.
  • Check the display — has your Mac failed to start up, or has it started up, but you just can’t see anything on the screen? Modern Macs don’t chime when they start up, so it can be difficult to tell. If you’re using a Mac mini or a Mac Pro or have a laptop connected to an external display with its lid closed, make sure it's not the display that’s the problem. Check the connections. Try rebooting with the display switched off and turn it on during start-up.
  • Try another user account — if the problem occurs after you type in your password to log in, try a different user account. If that works, the problem is likely to be login items or launch agents in your main user accounts.
  • Boot in Safe mode — if nothing else works, try booting in Safe mode by holding down Shift while it boots. That will boot your Mac with the bare minimum it needs to run and won’t load login items and launch agents. If that works, you know the problem is in third-party software that loads at boot time.

6. macOS Big Sur is running slow

This is perhaps the most common problem you’re likely to run into with Big Sur. It’s logical to assume that a new version of macOS should run faster than previous versions. And in some cases, that’s true. For example, Safari tends to speed up with every release. But new versions of the OS also put more pressure on system resources. 

So, if you have a Mac that’s a few years old, you are likely to encounter that the macOS Big Sur is running slow. There is plenty you can do to mitigate that, though.

Things that can slow down your Big Sur experience:

  • Undetected apps running in the background (login items)
  • Extensions
  • Old apps

If you have a free minute to investigate, you can once again use CleanMyMac X to disable login items that can considerably slow down your Mac at start-up and while it's running.

  1. Download a free edition of CleanMyMac X.
  2. Choose Optimization in the sidebar.
  3. Select Login Items. 
  4. Check those you don't need opening the next time you log in.
  5. Press Remove.
CleanMyMac X - Login items

Now, all those apps won't be opening as you start up your Mac. 

Check your Activity Monitor

Activity Monitor will tell you which processes are consuming more than their fair share of CPU cycles and RAM. Once you’ve identified those, you can decide if you really need those apps. If not, you can get rid of them, and that should speed up your Mac. Likewise, there may be login items you have long forgotten about that are running in the background, slowing down your Mac.

  1. Go to Applications >Utilities and launch Activity Monitor.
  2. Click at the top of the CPU column to order processes by the CPU cycles they are consuming. If there are any that are hogging the CPU and that you know you don’t need (only those that you recognize and understand what they do), select them, and press Quit Process.

If your Mac speeds up, you know it was that process that was causing the problem. If it’s associated with an app or login item, you can decide whether to uninstall it.

7. Apps are not launching on Big Sur

On the first day of the official Big Sur release, many users experienced problems with applications after they upgraded their Macs. Some reported apps not launching on Big Sur, while others complained about both programs and computers running slower than usual.

As it occurred, there was a problem with Apple's Online Certificate Status Protocol that failed to validate digital certificates for software on Macs. It disabled Apple's Gatekeeper, which in turn couldn't validate apps.

If you experience a similar problem again, first check whether everything's okay with the Apple Servers. Visit the official Apple Support system status page for the latest updates.

8. Bluetooth is not working on macOS Big Sur

Bluetooth is an essential feature on your Mac: it allows you to connect all your wireless devices and use your Mac more effectively. If you find out that Bluetooth is not working on your Mac after the upgrade to Big Sur, here’s a quick fix that could help:

  1. Press Shift-Option and click the Bluetooth icon in the menu bar.
  2. Select Debug.
  3. Click “Reset the Bluetooth module.”
  4. Press Ok to continue.

After the process is finished, restart your Mac as usual. The issue should be gone.

9. Wi-Fi problems on macOS Big Sur

Some of the users complained that Wi-Fi stopped working on their Mac after the upgrade. Here’s what you can do to fix Wi-Fi connection problems in macOS Big Sur.

The first thing you should do is forget the network.

  • Go to System Preferences > Network.
  • Select Wi-Fi and click Advanced.
  • Select the network you want to forget and press the “–” minus button.
  • Press Remove to confirm.

Next, you’ll need to reset SMC. This often helps to solve bugs related to power, battery, fans, and other features.


To check whether your Mac has a T2 chip, go to the Apple menu > About This Mac. Click System Report and select Controller. If your Mac has the Apple T2 Security Chip, there will be an "Apple T2 chip" on the right.

To reset SMC on Macs with the T2 chip

  1. Shut down your Mac.
  2. Press Control-Option-Shift and keep holding keys for 7 seconds. Your Mac may turn on.
  3. Hold the keys and press and hold the power button.
  4. Hold all those for another 7 seconds and then release.
  5. Wait a few seconds and then turn on your Mac as usual.

To reset SMC on desktop computers with the T2 chip

  1. Shut down your Mac and unplug the power cord.
  2. Wait 15 seconds. Plug the power cord back in.
  3. Wait 5 seconds and turn on your Mac as usual.

After you reset the SMC, reconnect to the Wi-Fi network. Things should be back to normal.

10. Battery drain on macOS Big Sur

Several users complained that their Macs were showing battery service required warning after installing macOS Big Sur. It can be frustrating, especially if your Mac is brand new and has only a few battery cycles. If you’ve noticed that macOS Big Sur causes battery drain, resetting PRAM may help.

PRAM (parameter random access memory) contains control settings and configuration of your Mac. Resetting PRAM can fix what’s wrong with desktop, keyboard, volume, or battery settings.

  1. Shut down your Mac.
  2. Press the power button and press and hold Command-Option-P-R keys immediately.
  3. Hold the keys until you hear a startup sound or until the Apple logo appears and disappears for the second time.
  4. Release the keys.

After your Mac starts up, your settings should go back to default, and the battery issue should disappear. If this didn’t fix your battery issue, you might need to revert to Catalina.

Sometimes certain apps may eat too much of the CPU and battery resources. You can identify such programs by using the Activity Monitor. It's best to delete such applications and see if it resolves the battery issue. CleanMyMac X can help you with that — it deletes multiple apps and removes all traces of the application. 

  1. Download a free version of CleanMyMac X (if you don’t have it installed)
  2. Choose the Uninstaller module from the sidebar.
  3. Locate the app you want to uninstall.
  4. Press Uninstall.

11. USB devices disconnecting randomly on Big Sur

This issue has been bothering 2020 MacBook Air and MacBook Pro users on macOS Catalina. The 10.15.6 update finally fixed the bug, but the macOS Big Sur seems to randomly disconnect USB connections too.

Disconnecting and reconnecting a USB hub may help. Some users resolved the issue by restarting their Macs. But this doesn’t fix the problem reliably. Hopefully, the developers will address this issue and present a solution with the next software update.

There are many ways in which Big Sur can run into problems. Thankfully, there are also lots of solutions. If you work through them step by step, you should be able to fix the problem. And using automated fixers, like CleanMyMac X, can help make the whole process much quicker and funnier.

12. Grey screen with mouse pointer on Big Sur

This is a newly found installation issue that many Mac users report. Trying to run the Big Sur installer the screen goes grey displaying a movable mouse pointer. There’s no way to proceed next.

The possible solution involves resetting NVRAM.

  • Turn off your MacBook completely. 
  • Turn it on again and hold down: Option + Command + P + R.
  • Keep holding the keys for 20 seconds.

Note: If your Mac has a firmware password enabled, the above combination won’t make the reset and your Mac will likely boot to macOS Recovery. To reset NRAM in this case, you will have to disable firmware password first.

To disable firmware password, run macOS Recovery > Utilities > Startup Security Utility.

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