F-Droid Repository
You can download Zettel Notes and my other android apps via the F-Droid client and receive all updates through it. You need to add this F-Droid repository as a third-party repository either by scanning the QR code or adding the URL manually (copy the link from below image): Verify that the repository details are:
Address: https://thedoc.eu.org/fdroid/repo
Fingerprint: B1358F5B942E5676B2935B83F39E3BAA363F3FDA9E53DB62113551D14B09A173