I use obtainium for my password manager and a few other apps, i also use f-droid for other apps. The way i understood it, is that f droid uses their own keys for signing apps, different from the source of those apps. But i may be mistaken on that. Also, i use graphene os, even though i believe burritos uninstalled it due to personal issues with the origonal copperhead creator. It still is, imo, the most secure os

You should check out "obtainium". You can install apps directly from source. https://github.com/ImranR98/Obtainium