GRUB boot to last OS

edit /etc/default/grub

change or aadd:

GRUB_DEFAULT=saved

GRUB_SAVEDEFAULT=true

GRUB_DISABLE_OS_PROBER=false

Recreate config

Arch example:

grub-mkconfig -o /boot/grub/grub.cfg

EFI BOOT ENTRY

DELETE

To delete a menu entry using efibootmgr
first list the current boot entries with sudo efibootmgr
Identify the boot number of the entry you want to delete, then use the command:
sudo efibootmgr -b XXXX -B
replacing XXXX with the boot number of the entry you wish to remove.

ADD

To add a menu entry using efibootmgr, use the following command format:
sudo efibootmgr -c -d /dev/sdX -p NN -L "Label" -l "\EFI\path\to\boot\file.efi"
where /dev/sdX is your disk, NN is the partition number,
“Label” is the name you want for the boot entry,
and \EFI\path\to\boot\file.efi is the path to the EFI executable.

!!! Make sure the path to the boot file is correct and uses backslashes, as required by the EFI specification!!!