> > > I cannot see any changes in /etc/grub.d/ or /etc/default/grub > It saves data in the GRUB environment block
https://www.gnu.org/software/grub/manual/grub/grub.html#Environment-block Somewhere in /boot/grub/grubenv but I think firmware storage may also be used To use it, you must set GRUB_DEFUALT=saved https://www.gnu.org/software/grub/manual/grub/grub.html
