You are able to host all these services and more on the same domain. I do a similar thing with different services at different subdomains. I don’t believe the username@ portion can help point to different services, that syntax is usually associated with email addresses.

I think the best way to go about it would be having different subdomains such as lemmy.domain.tld, matrix.domain.tld, etc.
To accomplish that, I have a wildcard subdomain point to my server, my reverse proxy (Caddy) handles figuring out which subdomain maps to which service on top of handling TLS certificates for me.