mosquitto Error: Address already in use

you can run following to check which ports are in use and by which application

ss -tulpn | grep LISTEN

as well you might be impacted by this https://dietpi.com/forum/t/7-0-2-upgrade-mosquitto-doesnt-appear-to-work/5122/1
because I see following on your output

Starting in local only mode. Connections will only be possible from clients running on this machine.