if disabling secure boot didn’t work, try this, so UEFI loader has an easier time finding Qubes OS:
- stick your Qubes drive back into your old computer and boot
- open terminal in dom0 and run:
sudo cp -r /boot/efi/EFI/qubes /boot/efi/EFI/BOOT
sudo mv /boot/efi/EFI/BOOT/grubx64.efi /boot/efi/EFI/BOOT/BOOTX64.efi
- power off the old computer, stick the drive into the new one and try to boot
adapted from the accepted solution of [MSI PRO H610M-E DDR4] Cannot boot Qubes after a successful installation