System76, Framework, even Dell officially supports Ubuntu in limited cases.
I’d just try a couple different distros and see which one has the fewest issues for you. If you like, you can pay for official support from Dell or Canonical. If you do identify an issue in a supported scenario (Ubuntu version + device model) they will actually help you troubleshoot and resolve the issue. RHEL is the same if you want to pay a bit more.
How much storage are you actually using? You could just split it between the r230s and set up zfs replication in proxmox.