Looking for an informed opinion; what are the practical consequences for European companies using American cloud providers (which I guess is most of them) ?
Immediate consequences... None. While all of your competitors are still using american cloud services, you won't get fined.
But as soon as competitors start moving to european hosting solutions, you need to too - because if you're slow to move over you can bet the courts will be chasing after people with fines.
in my opinion, most european companies are not using the cloud (especially if they are not in the tech space).
Colocated hosting is very, very large in europe, and many small/medium bussinesses operate out of a couple of VM's on a server in some datacenter, usually managed by some MSP.
Also, Egress fees are very expensive in the cloud, especially if you look at the cost of data transfer inside colocated facilities.
data transfer in the US seem expensive even if you look at colo/private circuits compared to europe.
But as soon as competitors start moving to european hosting solutions, you need to too - because if you're slow to move over you can bet the courts will be chasing after people with fines.