Hello Sebastian,
Actually, we are somewhat

VAG-COM - oh wait, that's now called VCDS - dependent.
And actually, there's also no support for the competition.
I think, however, that we can consider Diamex as an exception.
There was a period in the airbag control unit (STU) field where these units could be permanently affected by diagnostic tools.
could damage it (if I recall correctly, late nineties). It's possible that your vehicle falls within this timeframe, and Diamex may have omitted the critical parts or disabled certain functions as a precaution.
Generally, safety-critical components have notches.
My suggestion would be to have the engine control unit (ECU) checked using a VAG diagnostic tool (e.g., at a workshop) or a...
Have the latest VCDS version read out.
Best regards,
Rudi