I just upgraded my Proxmox to 9 last night, too!
…from 7, 'cause that’s how long I’d been neglecting it. 😅
I’ve also been trying to get my old dual-Opteron server working again, after having abandoned it a couple of years ago due to what I thought was a bad motherboard (IIRC, it wasn’t turning on at all). I was gonna buy a new motherboard since I happened to run across a cheap Ebay listing, but I decided to double-check the existing one first, and lo and behold, it booted!
Then I tried to update the ancient Proxmox on it from 6 to 7, and now it still turns on but doesn’t successfully boot.
Also, I can’t get it to boot from a flash drive for some reason, so I think I might have to take out the SSD, reinstall Proxmox on it from a different system, and then put it back in.
What software would that be? I’ve been looking for a viable self-hosted alternative to Mint (and now Monarch Money) since forever.