sudo pacman -S linux-lts
# acpi_call-lts is necessary for acpi_call to work in lts kernal

EDITOR esp/loader/entries/arch-lts.conf
bootctl update

sudo EDITOR /etc/default/grub
    GRUB_DISABLE_SUBMENU=y
    GRUB_DEFAULT=saved
    GRUB_SAVEDEFAULT=true
grub-mkconfig -o /boot/grub/grub.cfg