If you want to be notified of updates for Amethyst grab the release URL and add it to Obtainium. You can use it to track and update apps from GitHub, F-Droid, HTML and more.

https://github.com/imranr98/obtainium

F-Droid has other issues and while they are making progress they admit they have technological debt, read about them here: https://privsec.dev/posts/android/f-droid-security-issues/