If you are on the big cloud providers, can't you consider flipping the problem and move ALL your data to the EU and apply all the requirements to all users as if they are ALL protected by European law?

You will have a one-time cost to migrate things, and depend on how many customers you have it may require you to add some automation to your systems (e.g, for the cases where a customer requests to get a copy of all their data, or to delete all the stored PII), but speaking as someone who had to deal with this in two different projects, I still think that taking this route was easier than trying to special-case everything based on user-specific citizenship.