APS moved away from OpenKeychain to PGPainless some time ago, from before this fork started. While not perfect either (see https://github.com/agrahn/Android-Password-Store/issues/287), PGPainless is being maintained, and from what I can tell from this APS fork’s git log, is automatically bumped via their renovate bot (e.g. https://github.com/agrahn/Android-Password-Store/commit/9a6b596199d7eb87b40b53c4cb111ba7a5b48188)
Did you see the Documentation section in the README.md? You basically initialise a password store on your server, and you use an implementation like this to sync (SSH + git) your passwords, which are encrypted via your GPG key.
https://www.passwordstore.org/ has some instructions how to initialise a password store on, for example, your server. Then refer to https://github.com/android-password-store/Android-Password-Store/wiki/First-time-setup to configure the app.
I was too! I almost migrated to Vaultwarden, but I’m very thankful this fork is continuing the original maintainer’s work.