check all option in your UEFI
SecureBoot off
Fast Boot off
No CSM
No Legacy
all disks on AHCI
you can check in terminal
inxi -Fxza
test -d /sys/firmware/efi && echo efi || echo bios
sudo efibootmgr -vSo first , 2 ways ,
-
backup , then format GPT , restore backup , chroot for update UUID & /etc/fstab
then you can install Grub2 EFI -
try with gpdisk or gparted but you need in this case to create a /boot/efi with flag boot&esp in vfat ( fat 32 ) min 33Mo to 100Mo
see this
https://serverfault.com/questions/963178/how-do-i-convert-my-linux-disk-from-mbr-to-gpt-with-uefi
for step 6 you have to be only UEFI , dont forget to update UUID on /etc/fstab ,
you will need to create dir /boot/efi , have UUID /boot/efi in /etc/fstab updated , then restore GRUb EFI