Check this out https://www.securemessagingapps.com/

For us it all comes down to Threema vs Signal vs Simplex. I think Matrix leaks too much metadata and the onboarding is a mess.

Threema has a bit of an advantage for us due to no phone numbers required for accounts.

Simplex could fit our use case also but the battery drain on users with Android and specifically running GrapheneOS is huge…