I am using 3 screens, besides the standard power supply also an external one on the usb-c. A picture would say everything but here there is no possibility.

I tried it too, but never got a result

Can you explain it better? i just found out that in order to use the third HDMI on the top maybe i have to supply it with energy with the USB/C next to it. The problem is that i have only one usb c port in my laptop! Any suggestions?

It didn't work for me straight away either.
Sometimes the devices are not recognised immediately. You have to wait or restart.
In the end it worked for me with trial and error. But I don't know why.