Debian.
For a server, you want something very stable. Stable, in terms of "How often does it get updated?", not "It doesn't crash".

As a desktop OS, Fedora is great and a good middle ground between "New enough to get the latest technologies" and "Stable enough to let the devs fix minor issues before next release".
Debian on the other hand gets upgraded only once every 2 years or so. For desktop use, this would get stale very quick, but for servers, not changing much is great.

If you want "Fedora", but for a server, check out AlmaLinux (/RockyLinux), which is a clone of RHEL. It's a super stable Fedora basically.

I really like the concept of CoreOS, but for my taste, it's changing too much and I, as a noob, am too afraid I can't get some self hosted services running on an immutable OS.
For my use case, Debian is my pick. For yours, I don't know. You could specify your use case better.

As desktop OS on the other hand, Fedora Atomic is a wonderful choice!

You should crosspost to !Selfhosted, there would be more people ready to answer.