Matrix is not a good platform. Especially as a discord replacement. All clients suck in their own unique ways, and so does server software. It doesn't have any meaningful moderation tools. It doesn't have half the user facing discord features (like streaming or functional pins). The search sucks.
You're not getting out of the corporate hellhole that easily
None that aren't at least in some way corporate. Maybe in another life, who knows. Or in a few years we'll have something that's actually useful and not corpo owned. With that out of the way, I've heard of but not tested these two: