Auto select last boot entry in grub2

Detect other os

install os-prober

/etc/default/grub

GRUB_DEFAULT=saved GRUB_SAVEDEFAULT=true

update

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

ubuntu

sudo update-grub

Arch

install grub uefi

grub-install --target=x86_64-efi --efi-directory=/boot/ --bootloader-id=GRUB

make config

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