@Sushi
Hi, can you please paste the output of:
getent group pihole
dpkg --get-selection php*
Which webserver do you use? if you did not actively chose one, it is Lighttpd.
Hmm just by chance I see that the dashboard looks the same like here: "Unable to complete update" [occured when running pihole -up]
In that case the update didn't finish, so not sure if there are any similarities, but for completeness...
And a second one with same symptom: See no stats after update to 5.0
There it is clearly that users chose a different webserver where Pi-hole installer then does not grant the required permissions. However DietPi v6.29 patch includes the permissions patch.