If you have another Linux alongside Qubes OS installed on the same disk and this Linux was set as fallback UEFI then after updating grub2-efi-x64 in dom0 it won’t overwrite your other Linux BOOTX64.EFI file but create a separate file BOOTX64.EFI.RPMNEW and you should overwrite BOOTX64.EFI with BOOTX64.EFI.RPMNEW manually if you want to boot Qubes OS when you boot from your disk:
That is considering you’re using the same EFI System partition for both Qubes OS and your other Linux.
I’m not sure what happens if your disk has multiple EFI System partitions.