Thank you for your answer. I can neither boot from legacy mode nor from efi.
I think this is because there is no efi boot partition with a GPT partition
table correctly installed on my hard drive.
I will try with Debian testing.
On the french forum we have found this wich is particularly suitable
https://www.forum-des-portables-asus.fr/forums/threads/plus-de-choix-windows-boot-manager-pour-booter-uefi.8316/page-3
It gives informations on how to recover the disabled SATA HDD. If it works I
will traduce the info here.