MQTT Transmission - Connection (to broker) PROBLEM

Dear readers of the current topic,

I have an issue to connect to an MQTT Broker with the MQTT Transmission module on the physical server (see next picture):

The firewall was turned off temporarily, so that should not be the problem.

I tried to do the same thing on a Virtual machine with Ignition trial version, and there it was working without an issue:

Someone can give me some suggestions or solution what can I try to solve the problem?!

Best regards,
Arnold