So it's not acceptable for a EU company to store any customer data with a US company? They very literally all do. We are also not the US, and are I'm sure happy to arrange a sensible agreement. Regardless I still don't think this is the big issue that some europeans make it out to be, back in the real world I don't think we've lost any customers due to brexit. I think the friction in gaining new ones from the EU is purely psychological "but brexit makes that hard" or "but you're not in europe, /yes we are/ oh you know what I mean".
So it's not even a theoretical issue, it's a well-trodden path from attempts at trade-deal guaranteeing things with USA.