- Under the VM's
Hardwaretab, changeBIOSfromDefault (SeaBIOS)toOVMF (UEFI)in the Proxmox web UI - Click
Addat the top and selectEFI Disk. Select a location and click OK. - Boot the VM using Boot Repair Disk. Alternatively, boot any live CD and install the Boot Repair tool. Instructions for Ubuntu here: https://help.ubuntu.com/community/Boot-Repair
- Use Gparted or your favourite partitioning tool to create an EFI partition. Note: You may need to resize your disk and adjust your partition layout.
- Run the Boot Repair tool and choose the recommended option. Follow the instructions
NB: This works on a disk partitioned using MBR.