But if you want to use Ardupilot that FC is supported. Copter version here try using Load Custom firmware after downloading the .apj file. This assumes it’s the Pixhawk4 Mini from HolyBro. https://firmware.ardupilot.org/Copter/stable/PH4-mini/
thanks for the hint. Unfortunately this does not solve the problem why two of the engines stop when I accelerate. The other two continue to run without problems.