OpenHAB3 MQTT Configuration with Text Files on Windows 10

Setup, Configuration and Use Migration
2

It’s of no use at all in OH3

You can’t. It’s simply not supported in OH3.

I don’t know where you got that, it’s nonsense.

What you have to do -

Install MQTT binding

Add a broker bridge Thing (not a System broker,just a broker) to connect to your MQTT broker.

Add various Things, roughly representing each device or service you will use.

To each of these, add channels for each piece of data, configuring there topics to subscribe to, topics to publish to, and transformations required.

These channels get linked to your Items.