http://192.168.0.100/html/admin does not work neither (404), and as mentioned, htop does not show pihole running. Any way to use the old installer/setup?
(But typing pihole at the command promt at least show
root@DietPi:~# pihole
::: Control all PiHole specific functions!
:::
::: Usage: pihole [options]
::: Add -h after -w (whitelist), -b (blacklist), or -c (chronometer) for more information on usage
:::
::: Options:
..so something is installed, somewhere.

However:
root@DietPi:~# pihole -d
/usr/local/bin/pihole: line 41: /opt/pihole/piholeDebug.sh: No such file or directory