s/mod-probe/os-prober/
OP, you are wanting to do a fresh install of proxmox on the disk that has your ubuntu? If so then you should have a full backup of that ubuntu bc the proxmox installer wipes the entire disk and replaces it with Debian.
If you don't want that disk wiped, then you could consider installing Proxmox on an external USB3 SSD such as a Samsung T7. Then to access your other boot partitions you would probably have to install the os-prober package and enable same in grub config. This is admittedly a bit of a complex adventure, so if you have a separate machine for Proxmox I would install it there instead to keep things simple(r).
Accessing your win11 in proxmox by not doing a P2V is not recommended, win11 could get confused with the different hardware profiles -- physical hardware vs VM environment.
I would recommend doing a bare-metal backup of your win11 with Veeam free agent and restoring it into a VM if you want to run it in proxmox.