I have a couple of non-crossplay servers running without issue.

I run under docker using this image: https://hub.docker.com/r/lloesche/valheim-server

which makes it very easy to install. The only thing you have to do, other than running the commands they specify is to punch the right holes in your firewall (server, if it is running a firewall, and router firewall, of course).

I have no way of testing crossplay, so I have no idea how that works.