I am not a professional, but i would say you can probably remove the App, BUT with just removing the App it might still be somewhere on the phone on a deeper level that you cannot really see right away and is hard to trace.

Be aware, its not completely FOSS: https://github.com/toeverything/AFFiNE/blob/canary/packages/backend/server/LICENSE

There is an Github Issue: https://github.com/mullvad/mullvadvpn-app/issues/8737

Yep.

I am in the process of buying a phone to run Linux on. The App i am building (in Flutter) will even target Linux and Android Phones, so that i can jump ship if android goes to shit.