TLDR: The r/selfhosted subreddit has a Discord server. The owner’s account got hacked leaving the server in a precarious state. They submitted a support ticket, but Discord has not taken action in weeks and probably won’t at all, so they are considering starting a new Discord server.
I’ve never self hosted a discord alternative, but it doesn’t seem like it’d cost anything to just spin it up beside existing self hosted infrastructure.
Here is some advice then: Don’t run a public service until you understand the risks and are capable of protecting yourself and your users. It isn’t as simple as booting up a service for self use. By using Discord they minimised damages to users it would be worse if they lost control of a Discord alternative with RCE exploits.