Okay, so I’ve just signed-up to help you (maybe lol)
Just got it working, it’s important to use UEFI (with EFI disk for uefi storage ofc) and disable secure boot:
ESC (as soon as you see the proxmox logo) > Device Manager > Secure Boot Configuration > Attempt Secure Boot - press space to remove the X
Just exit / reset and it should reboot straight into the installer