After installing PVE 8.1 successfully from its ISO on my R810, I have now edited /etc/apt/sources.list and added
deb Index of /debian/pve/ bookworm pve-no-subscription
and after saving the change, did an
apt-get update;apt-get upgrade
and I now am running Proxmox 8.2.2 official successfully on my R810 where it WOULD NOT install from the Proxmox 8.2 official ISO.
So for my particular Dell R810 with the PERC700H RAID controller, it definitely works to install Proxmox VE 8.1 official ISO, then do an after-the-fact apt-get update;apt-get upgrade to get it to Proxmox VE 8.2.2 on that same hardware after editing /etc/apt/sources.list and adding the above line.