o.k. so we tried to upgrade a latest PVE 7 to 8 with bullseye to bookworm.
Box is a hpe proliant, Xeon, 16GB RAM, 4x 4TB HD min. 50% free, was last set up a couple of month ago, worked fine, all updates installed.
Duly followed https://pve.proxmox.com/wiki/Upgrade_from_7_to_8
pve7to8 --full...