A German court would use judicial assistance and ask US law enforcement to help. US law enforcement would then adhere to local laws and protect the rights of US citizens while trying to help.
This is named Mutual legal assistance: https://en.wikipedia.org/wiki/Mutual_legal_assistance_treaty .
If you talk to actual people in Europe, outside of HN, you’ll find that overwhelming majority of people do not give a flying fuck about the “safety of their data” from US government. They just blissfully post shit on Facebook with no care in the world. This matter is a concern mostly to politicians and to activist hacker types.
This is not to say that this is not a valid concern to have, but I’d like people to spare me pretending that it’s about politicians caring about people’s rights, when just past few years they trampled all the rights in the interest of fighting coronavirus (and if you want to argue that it was all worth it, because the goal justified the means, keep in mind that the US government can say the exact same thing about its data access!). This is just standard power politics, a protectionist trade war whitewashed with talk about “rights” and “privacy”, only surprising thing is how people on HN are gobbling it up. I guess maybe that’s just willful ignorance - by pretending you don’t understand why EU actually attacks American companies like that, you might actually get some extra privacy protections you care about.
If you think a warrant should apply from an outside jurisdiction imagine Mississippi issuing a warrant to arrest a Californian abortion doctor.