> Could someone explain to me how this should work?

I think the general idea is that Facebook and co. will need to spend their lobbying influence and dollars on getting FISA and the CLOUD act changed to allow them to make the necessary privacy and integrity guarantees for the European user data. And/or for the US to make those changes to get or keep the same kind of market access.

The former is unlikely at best and the latter would require the kind of "giving in" that the US gov does not like to do. I think continual can kicking or eventual EU capitulation is more likely.