It worked, steps I took to restore a snapshot through live usb using btrfs-assistant and systemd-boot.
- Boot to live USB
- Update mirrors through Welcome app
# pacman -Syy
# pacman -S snapper
$ yay -S btrfs-assistant
# mount /dev/sda2 /mnt -o subvolid=5
# cp /mnt/@/etc/snapper/configs /etc/snapper/configs
# cp /mnt/@/etc/conf.d/snapper /etc/conf.d/snapper
Then, open btrfs-assistant and restore the snapshot…