I used snapper until it was broken.
Then I switched over to # btrfs subvolume snapshot ...
You take the same steps with # btrfs as # snapper rollback does
1) create a read-only snapshot of the actual root subvolume.
2) create a read-write snapshot of the previous working read-only snapshot.
3) set this snapshot as default subvolume ( # btrfs subvolume set-default ...)
Then you chroot into the new default subvolume and
1) install grub ( # grub-install )
2) recreate the initramfs ( # mkinitcpio )
3) recreate /boot/grub/grub.cfg ( # grub-mkconfig )
That worked. No need to edit grub.cfg manually.