Newbie: Laser connected and working but not engraving

Hi,
I am new to Lightburn and installed the Lightburn 2.0.05 on Windows 11. I have a ComMarker Omni X UV Laser 6W with a 150x150 lens connected via USB.
Now I want to test engraving something. I drew a rectangular. and tried to engrave it into MDF.
The green preview helper showed where the rectangular would end up, the laster was running as expected but there was nothing engraved.

I used settings:

These are the values recommended in the OmniX operations manual for the 150x150 lens for engraving wood.
Now, I let it run again continously for 100 passes, and then I could see a faint rectangular in the wood. So the laser works, but seems to be too weak.

UV lasers do not have any power settings. How can I adjust the output of the laser?

I attach my device settings:


Note: ComMarker Studio works fine with the same values for speed/pulse/frequency and the same focal distance.