This was a very nerve racking experience as I'd never gone through a major version Proxmox update before and I had spent a lot of time getting everything just so with lots of config around disk and VLANs. The instructions were also a big long page, which never fills me with confidence as it normally means there's a lot of holes to fall in to.

My initial issue was that it says to perform the upgrade with no VM's running, but it requires an internet connection and my router is Opnsense in a VM. Thankfully apt dist-upgrade --download-only, shutdown the Opnsense VM and then apt dist-upgrade did the trick.

A few config files changed and I always hate this part of Debian upgrades, but nothing major or of importance was impacted.

A nervous reboot and everything was back up running the new Proxmox with the new kernel. Surprisingly smooth overall and the most time consuming part by far was backing up my VM's just in case. The upgrade itself including reboot was probably 15 mins, the backups and making sure I was prepared and mentally ready was about an hour.

Compared to upgrading ESXi on old hardware like I was doing last year, it was a breeze.

Highly recommended, would upgrade again.