Quick google:
Number of discord users: 150M
Number of matrix users: 60M
Go where you can reach the most people. Not saying I like it. It's just the way it is.
It's a negative trend that all the collective knowledge of these communities end up being siloed in platforms that can't be accessed from the open web.
I wouldn’t even know where to setup a new Matrix server, I suspect it’ll involve installing server software but is there a larger instance of Matrix people use? (Akin to mastodon.social)