Brake performance almost zero - extremely penetrated...

Moin moin,

I have a real problem. Had hardly any braking performance from today to tomorrow - stuck sonast almost to the disc, when I braked, now it only brakes properly at first tap but if I want to brake properly from the ride, I really have to laugh on it, and even then it is an almost insufficient braking performance. Was with the screwdriver, clearr brake was flat, so new from ATE.
Trotzdem is dat Bremsverhalten unter aller Sau.
When I put the brake on, do I hear a kind of noise/hiss from the front - brake booster?
Does that have any security... I mean to rule out such little things as a cause?
When changing, the brake system net was opened - only the "stamps", which push the jaws back to the disc, so that the coverings fit in. So there's nothing to be aired, right?
For helpful answers thank you in advance