I don't know much about "mostly", but check out the channels on the server kde.org, where they do discussions regarding visual design, development, documentation and all that good stuff.
Sometimes, if you mostly find what you don't like, you might be looking at it from the wrong angle. For instance, I found a few, very desirable communities on Reddit, so much that I am finding it hard to leave. And that is the few that I searched for. Only realised the toxic communities, when I read others' rants on it ^[and from the recommendations. Definitely don't checkout the Reddit recommended communities or you will get said toxic stuff.].

This is really not accurate. Matrix is not designed to be a super privacy first protocol. It's like Lemmy in the it's designed to solve a problem and be a useful federated collaboration tool. It borrows features from a number of popular messaging platforms. Message history is stored on the server but encrypted client side so privacy is preserved. It supports group chat rooms. It supports voice and video. And most importantly, it supports bridges- you can connect your matrix to other services that are completely incompatible with matrix using a bridge. Perhaps the best example of this is Beeper, which is built on matrix. They are trying to replicate the user experience of the old app Trillian- beeper can link with a number of chat services including Google messages, slack, WhatsApp, telegram, signal, etc. Thus you get all your chats in one place.