which OS for a homelab?

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.

Debian and Proxmox

I have heard good things about proxmox (it's based on Debian), might be worth a look

Been using nixos. High learning curve but having everything to remake the system in version control is really nice.

I've been using Fedora Server for over a year, now, with many podman containers and haproxy. No problems till now.

If you are going to be treating your server as a pet (server down services down) and not cattle (node that can disappear) you are going to want to stay away from images hat require a reboot to update.

Assuming pet based on limited context.

Debian stable or testing as the most "cutting edge" is what I'd suggest but ultimately any package updatable stable lifecycle distro you are comfortable with will work. Most of what I do is use debian stable and docker to run all the services which you can on basically any distro.