For some a Discord alternative needs to be a voicecall, for others it‘s game streaming, and for others it‘s just a chat, a bulletinboard or newsgroup, while they never used the Voice features.
Doesn't Matrix essentially satisfy all of them?
Although the bulletinboard/newsgroup feature is something that I don't know but I feel as if that can be on matrix as well.
Yes, I know Matrix is hard to host but I don't imagine discord if they release their source code to be easy either.
So for a discord-like experience, I really prefer matrix.
It has voice calls and meetings but that's not the same thing and has much higher friction to use.