Signal started marking their releases as "pre-release" on Github:

GitHub

Releases · signalapp/Signal-Android

A private messenger for Android. Contribute to signalapp/Signal-Android development by creating an account on GitHub.

Reason why those are not showing up as latest on Zapstore. We used to fetch pre-releases, at that time a Termux pre-release screwed up lots of setups. Pulling pre-releases then needs to be evaluated on a per-project basis, this is hard.