The “remove Session” thread started over a year ago in June 2024 and it was said it’s likely to be removed nearly half a year ago in January 2025. In that time there hasn’t been any progress on removing Session, so for the foreseeable future Session is likely to be the best backup. Threema is another great messenger and is recommended by Techlore, but it’s paid.
I already touched on the security issues with Wire and XMPP but I don’t think the community has scrutinized Keybase yet, which would be worth discussing in its own thread.