Please follow the below template, it will help us to help you!
If you are Experiencing issues with a Pi-hole install that has non-standard elements (e.g you are using nginx instead of lighttpd, or there is some other aspect of your install that is customised) - please use the Community Help category.
Expected Behaviour:
FTL is online
Actual Behaviour:
FTL failed to start due to failed to creat listening socket for port 53: Address already in use. I can't find in the logs what process is already using port 53
*** [ DIAGNOSING ]: Ports in use
(...)
[53] is in use by dnsmasq (https://docs.pi-hole.net/main/prerequisites/#ports)
[53] is in use by dnsmasq (https://docs.pi-hole.net/main/prerequisites/#ports)