Bug#902928: Cannot bring the grub menu up with Shift key along with GRUB_TIMEOUT_STYLE=hidden with GRUB_TIMEOUT=0

[Andrey Butirsky]

Works fine on my UEFI system.

I was needed to do some preparations described here:
https://wiki.archlinux.org/title/GRUB/Tips_and_tricks#Hide_GRUB_unless_the_Shift_key_is_held_down