Recently I'm actively seeking replacement for telegram, since it's not reliable anymore (taking free user's account without any notification). I have tried matrix. It sounds good, but your experience mainly depends on your home server. I set up 3 accounts on matrix.opensuse.org, matrix.qoto.org and matrix.org. The experience is different. The matrix one is the default one, as expected, I need proxy to connect it, beside that, everything works fine. The qoto one is not that smooth, there are lags and errors during my test (matrix.org server cannot connect to the qoto server, I don't know why). The openSUSE one is pretty good, I use their matrix service for almost a year, and the most important thing is I can directly connect to it without using any proxy in China. So, I delete my other 2 accounts and keep using the opensuse one.

Today, Google play recommended me an app called ThreeMa. A one time paid app which offers a full anonymous communication. It don't need any private info to register (while matrix use email, opensuse server use their own SSO login). And it's also e2ee, just like matrix, it also support file, video call etc. And to my surprise, it's not banned in China, I can send message to the echo account without using any proxy (but might be blocked in the future).

I guess they are my current backup communication app for now.

(Also, Briar did a good job too, it can make communication happens only using Bluetooth, WiFi or internet over tor, but it only works on Android, and doesn't have any advance features, it's a good replacement when internet is down or we lose internet access like North Korea)