It is much more complicated to host a Matrix homeserver and Facebook Messenger bridge, however, it allows you to use a FOSS chat app on your Android phone. With notifications and if needed, fully outside google infrastructure, or even fully selfhosted, with ntfy.sh for example. Without running any proprietary Facebook code, and without directly connecting to Facebook servers on your Android device.
It is of course unavoidable to have complete privacy, as your messages will still be sent to Facebook, but you avoid almost all telemetry (and all on-device telemetry) by using a Matrix bridge rather than the official website/app.
Another option is Beeper, although privacy with them is questionable, since you’re fully trusting them with your account, and any incoming/outgoing messages. It does avoid Facebook telemetry on device, and is much easier than hosting a Matrix homeserver.
Short answer: you don’t. It’s either privacy or a facebook app, not both.
Longer answer: Don’t use the facebook app https://github.com/mautrix/facebook (requires your own Matrix homeserver)
It is much more complicated to host a Matrix homeserver and Facebook Messenger bridge, however, it allows you to use a FOSS chat app on your Android phone. With notifications and if needed, fully outside google infrastructure, or even fully selfhosted, with ntfy.sh for example. Without running any proprietary Facebook code, and without directly connecting to Facebook servers on your Android device.
It is of course unavoidable to have complete privacy, as your messages will still be sent to Facebook, but you avoid almost all telemetry (and all on-device telemetry) by using a Matrix bridge rather than the official website/app.
Another option is Beeper, although privacy with them is questionable, since you’re fully trusting them with your account, and any incoming/outgoing messages. It does avoid Facebook telemetry on device, and is much easier than hosting a Matrix homeserver.