I know btrfs alone doesn't replace unraid on its own, but it does replace or at least substitutes most of the raid functionality. Btrfs is extremely flexible and it's raid features are almost unmatched in capability for running in small environments where you may need to increase or decrease the number disks in an array at will and without much limitation.

If you want a gui to manage various linux systems, you could look into cockpit. It can manage VMs, containers and other linux systems via a unified gui. I would recommend fedora if you want to give it a go.

But you do you. I have not really had the desire to use unraid since i already know linux and manage the system myself without many tools, but i understand most people do not know linux that well and learning is a significant time sink.