thanks guys. I also tried a long time, so i give up now and get dummy plugs when i am back.

And just to be double sure and to understand:
I plug a monitor in now, change the settings (f.e. fan speeds/core voltage etc. in AMD settings), then - even when I boot later without a display - those settings still apply, right? I am just wondering because if the AMD settings don´t start in headless mode how can those settings be applied.