As someone who's (sadly) moving away from matrix due to the state of clients and running out of patience for Element X (it's been... What? Two years?) I have to say SimpleX and/or XMPP are where I am looking.
If you are willing to try out new things other than XMPP, I'd recommend looking at the NOSTR protocol and more specifically at the 0xchat client. They provide private message with E2EE but the biggest advantage IMHO is that you get connected to a huge variety of other services and people using the same protocol.
I find that better than building the connections on what are essentially closed gardens or, at best, isolated islands. Over there exist hundreds of servers (relays) run by volunteers where new features are proposed by users and actually implemented (success or failure depends truly on themselves).
Other good features being delivered on NOSTR are for example the anonymous IPFS (blossom files) where you can host complete static sites across the relays. There is truly plenty to discover there and to build, feels like the 90s and has been fun.
Not a great first impression.