@elverkonge It didn't get overwritten - it's a thing that sometimes happens when deleting a partition (e.g. a dual boot one), apparently; the UUID of the boot partition gets corrupted & the only way to fix it is delete it & create a new one, if you know how basically the partition is still there, but the missing header means the OS can't find it & since it's the boot disk, well... Thank you for your good wishes
