This isn't quite up to date. There are two newer OS versions out since this. Bullseye (11) and just released last week Bookworm (12).
Also an ancient version. We released V5 in May 2020, more than three years ago.
I would flash a fresh new OS (perhaps on a fresh SD card as well, since yours has some miles on it) and do a clean install of the current version of Pi-hole.