Jan 03 03:17:49 DietPi systemd[1]: lighttpd.service: Main process exited, code=exit
ed, status=255/n/a
Jan 03 03:17:49 DietPi systemd[1]: lighttpd.service: Unit entered failed state.
Jan 03 03:17:49 DietPi systemd[1]: lighttpd.service: Failed with result 'exit-code'
.
Jan 03 03:17:50 DietPi systemd[1]: lighttpd.service: Service hold-off time over, scheduling
restart.
Jan 03 03:17:50 DietPi systemd[1]: Stopped Lighttpd Daemon.
Jan 03 03:17:50 DietPi systemd[1]: lighttpd.service: Start request repeated too qui
ckly.
Jan 03 03:17:50 DietPi systemd[1]: Failed to start Lighttpd Daemon.
Jan 03 03:17:50 DietPi systemd[1]: lighttpd.service: Unit entered failed state.
Jan 03 03:17:50 DietPi systemd[1]: lighttpd.service: Failed with result 'exit-code'
I tried to restart the service but it's still failed.
The DietPi version installs the web interface to /pihole. You may have issues because you switched versions. Try a fresh install with only one of the two versions.