The EU would have to put the US on a list of "foreign adversaries", with whatever political fallout comes from that. Not saying they shouldn't, but there will be downsides.

Since controlling these platforms is probably the best ROI for swinging public opinion, I'm sure it's a matter of time before they get seized (one way or another) and redistributed to reliable political allies.

Would they? There are already data residency laws, and the US didn’t have to be on any foreign adversary list for those to work, right?

whether or not they formally put the US on such a list for trade purposes, clearly they see the US as such.