Yes — to both questions. You can still use Hider 2 if you have it installed, there are no changes in the app's functionalities.
Still, there's a risk of data loss and decreased stability when using Hider 2 with newer macOS versions. To avoid the risk, we recommend to "unhide" your files and folders, and copy your secure notes to other protected note apps as a backup option. You might also consider switching to any of these alternative apps and services: iCloud, Apple Notes, 1Password, or Encrypto.
For more details and instructions, see this support article: "Hider 2 no longer updated nor sold as of July 10, 2019."