I read the complaint and it seems to have nothing to do with the reject all button and is only about transparency and informed consent. They state that you cannot reasonably read all those privacy policies and thus you also cannot give informed consent.

At least that is how I understood it

Probably both.

If I understand it correctly giving informed consent for over 1700 tracking partners of a single page isn't realistic. You as a single person cannot be expected to truly understand what it is you are agreeing to when you click accept.

The issue is that even if you click "Accept" there is no reasonable way to infer that the user has given informed consent, because becoming informed would likely take days or weeks.

As such the conditions for data sharing are not met.