I've got the same! Trying to install it for the first time and I'm running into the same image.
I tried this: https://pve.proxmox.com/wiki/OVMF/UEFI_Boot_Entries
But the shimx64.efi file doesn't show. When adding the HAOS drive to BOOTx64.inf it shows up as a boot option; I move it to the top...