Oh, that’s clearly it, everything connecting from another machine is refused.
In my opinion, it’s a new default option.
EDIT:
After some reading and experimentation on my side, I managed to reproduce it.
A new option has recently appeared. Well, it already existed but the default behavior has changed.
By default, Mosquitto containers only listen on localhost.
To change this behavior, you need to add this to the Mosquitto config
listener 1883