Someone introduced Beeper to me: https://www.beeper.com

It can support 14 different IM apps and manage them in one app.

It's technically good, but I don't trust it, 1) not all IMs are e2e encryption, 2) if this beeper account gets hacked, then all of my messages are doomed.

It does have an option to self host, but at least for the Android app you need to register an account.

I'll keep an eye on it.