You are running another webserver besides Pi-hole's lighttpd on your RPi:
*** [ DIAGNOSING ]: Ports in use
[80] is in use by apache2 (https://docs.pi-hole.net/main/prerequisites/#ports)
You should configure one of them for a different port.
See e.g. Lighttpd daemon won't start - #11 by Bucking_Horn for a possible lighttpd configuration.