I use deltachat/arcanechat. It uses the mailchat protocol. There's also tox, simplex, matrix, xmpp(conversations) these can do e2e, you can self host it or use a public server, everything distributed through app stores can be compromised. Every app were you rely on a central server can be shutdown. You also don't know how the server software works of for example "signal", what data they collect. Although messages are encrypted you can still log metadata like when where iplocation, with who?

The problem i guess with thr alternatives is bad service in terms of audio and video chat. The benefit of ms teams for example is their huge cdn. it just works nearly all over the world. Whatsapp/discord is used by so many that it's difficult to stay in contact otherwise.

Used to recommend XMPP (lol) but even with whatever encryption the servers still know and control too much. Like who you are chatting with (entire contact book) and when, plus attachments most of the time. And there was also the jabber ru incident... Don't feel like pulling up the article rn but basically it got MITMed by one of the ISPs (counting the hosting provider as ISP), with a new valid TLS certificate and all.

Tox supermacy! What looser needs a backlog, pffff.

Don't use SMS. As it is unencrypted, the ISP have complete access over it.

It's not that difficult to remember which people use which messaging apps. I use Signal, Line, Whatsapp, Matrix, Telegram, heck even Instagram DMs with different people. I try to push people to Signal whenever I can though.