signal had firebase in old version 4.33.5, a one time wtf-oops thing and yes, hard to overlook or dismiss in any regard (especially with who endorses them, front page security/privacy/encryption genius names) but it does happen occasionally, esp reference apps from play store. but this is not why it is not offered in f-droid, if i understand correctly it is due to reproducible build issues.
also, please do see this great service, provided by Exodus Privacy (also app in f-droid, get it, run it, profit!
they show latest version tested as 4.43.8 that’s a few releases away from 4.33.5.
Signal has metadata concerns, and is tied to your phone number, so if anonymity is desired/required then it may be better to look elsewhere. Wire also has metadata concerns but is tied to your reg email, again, iirc so don’t use identifying email. I haven’t used briar (don’t really have cell phone for years until few months back, even now it is sim-less and I test and play with it over wireguard)
not sure if Tox is available on phone, but I have used the qTox fork from linux desktop and it worked great for me and remotes for chat and voice, including group. I also have no knowledge whether Tox/qTox has data/metadata issues but I assume it does and treat it as I do other comms tools I use (like riot.im desktop) which is to say not enough trust to share my best in the universe chocolate cookie recipe on