Hello Don't forget, on external disk, it is also necessary to write /EFI/ubuntu/grubx64.efi on /EFI/boot/bootx64.efi ( https://doc.ubuntu-fr.org/tutoriel/installation_sur_disque_usb#specificites_support_usb_efi )
Hello grubx64. efi on /EFI/boot/ bootx64. efi ( https:/ /doc.ubuntu- fr.org/ tutoriel/ installation_ sur_disque_ usb#specificite s_support_ usb_efi )
Don't forget, on external disk, it is also necessary to write /EFI/ubuntu/