Last time i checked last year there weren't many options to migrate to, mostly Matrix communities (which are not quite the same thing) and Revolt Chat (which is a non-federated but FOSS and self-hostable drop-in replacement for Discord). Revolt sounds like the logical route as it's clearly designed for just this exact role, but it seems it's still early in development and not yet ready for the average Discord user (looks like the voice functions in particular are still in development)
Has this changed or improved since then? I feel like the use case of "IRC servers, but modern!" should have been solved years ago but feels like it hasn't, i have lots of non-technical people who heavily use Discord who I'd love to rescue from it before it starts actively burning, a replacement that isn't complicated and has all it's features would be welcome.
Revolt seems like it would be a good replacement if it gets to a stable point.
Other than that everything else is nowhere within miles of being a discord replacement. The best option IMO would be a regular chat server like Matrix/Element or something, and Teamspeak or Mumble for voice. But you won't have streaming, screen sharing, etc.
Everything like Element, Jitsi, and so on are replacements for stuff like Slack, they don't have easy to use voice rooms or streaming or anything like that.