Hi Steffen,
Thanks for the support.
When I check with efibootmgr -v this is the Proxmox output:
Boot0001* proxmox HD(2,GPT,ca72790a-27b1-4118-80a5-c46fd6868c6c,0x800,0x100000)/File(\EFI\PROXMOX\GRUBX64.EFI)
From my interpretation its GRUB being used. Furthermore when I check the...