I think that numbers relying on self-identification from census can also be far from the actual genetic makeup of the American population. But after some searching I couldn't find any comprehensive study that tried to trace today's Americans to different European ethnicities. And I'm not sure if this is possible anyways, given that Europeans were mixed in many ways.
2012: 50.7 million Americans identified as German. 2022: 41 million https://en.wikipedia.org/wiki/German_Americans