I found these old notes which may help - I was using a Dell Optiplex Micro to host Proxmox running a server 2019 VM with ROK license.
Replace <vmid> with the actual guest VMID
Create the VM but do not start it
In the host shell
cp /etc/pve/qemu-server/<vmid>.conf to /etc/pve/qemu-server/<vmid>.conf.ori
nano /etc/pve/qemu-server/<vmid>.conf
edit this line
smbios1: uuid=26844c41-fa3d-4b3c-9204-abc123abc123s2
to
args: -smbios type=11,value=x -smbios type=1,uuid=26844c41-fa3d-4b3c-9204-abc123abc123s2,manufacturer=Dell\ Computer\ Corporation
where x is a literal 'x'
and save the .conf
Start the VM setup as usual