In any situation, if somewhen your bootable device is not found on grub.
Try booting into qubes os installation media and boot into rescue qubes os entry.
Just skip to shell :
Then run efibootmgr -v -c -u -L Qubes OS -l /EFI/qubes/grubx64.efi -d /dev/nvme0n1 -p 1
-d = where your bootloader device remain.
could be : /dev/sda /dev/sdb /dev/nvme0n1 /dev/nvme1n1
-p = which partition.
you can try run lsblk first before running above command.