Move to XMPP. It's been around long enough to see it's not going anywhere, unlike the rest, and the modern server-client combos have all the needs - e2e encyption, message sync, etc - covered. It's also federated and you can run your own, but you don't have to.

You can start at, for example:

- https://account.conversations.im/ (8€/year)

- https://quicksy.im/ (free account)