Trying to re-configure MQTT following a major update - unable to connect

Hi all, I have just updated my home assistant to the latest version and now my MQTT is all broken. I have searched the forum and my understanding is that i should go to Devices & Services → MQTT → Re-configure which is what i did.

My home assistant and MQTT are all individual docker containers installed on the synalogy - and a while back when i create the MQTT containers using docker-compose. There are no username and password.

When i tried to re-configure MQTT, it says " failed to connect" - I am not sure if it is complaining about username and password (which there arent any) - or is this related to something else?

Any ideas? Helps much appreciated.