MQTT messages from Arduino to Homey

I would like to send repetitive water flow sensor values from my ‘Arduino Uno R4 Wifi’ to Homey. Unfortunately Homeyduino does not seem to work on the ‘R4 Wifi’ so I want to try it with MQTT messages but I am not familiar with this.
I have installed the MQTT -broker and -client on Homey and configured them according the Cornelisse YouTube videos but I don’t know how to proceed. Anybody can help?

You need to run software on your Arduino board that will publish the sensor values to the MQTT broker.

Thanks, I already found sketch code to publish the values but how do I refer to the broker on Homey?

By its IP-address.