Literally every single time I see people shilling a "privacy chat app", there are 1000s of them, and they all tend to be "more private than every other private chat app", only to then turn out that they're all either iOS and Android only, or iOS and Android first.

This alone immediately voids all claims of being "more private" than things like XMPP, or some other PC-first, battleground tested chat protocol.
Phones are never meant to be private, even if you install something like GrapheneOS, you're still dealing with the fact it's connecting to cell towers, the fact you can't swap out battery, the fact there are all sorts of anthenna's that can be exploited without your knowledge or concent, the fact it has unmutable microphone, the fact it has multiple camera's on 2 sides barely anyone considers taping, because their phone doubles as a video/photo camera, and so on.