> Backups?

Everything that works on desktop GNU/Linux should work on the phone, too. I use Pika Backup app.

> communication

AFAIK none of the apps you listed officially support Linux ARM, so you have to go through some configuration unfortunately. I do not use any of them, I use Matrix.

> Signal

https://forums.puri.sm/t/signal-app-now-usable-in-portrait-m...

https://framapiaf.org/@lolgzs/113010288224110061

> Whatsapp ... Discord

https://forums.puri.sm/t/how-to-install-whatsapp-and-discord...

https://forums.puri.sm/t/librem-5-web-whatsapp-com-not-worki...

https://source.puri.sm/libremos/tasking/-/issues/1

> Media

Are you talking about watching videos and listening to music? It works fine.