Huh. I'm trying to think, because that's a good point. Have I?

I mean, it's not like I've never heard something like "my father was from Germany", I definitely have, particularly when prompted. But "I'm half German"? That's more specific, and I genuinely can't think of an example of people who weren't dual nationals themselves. It gets complicated, too, because Americans tend to think of ethnicities as nationalities, but Europeans don't. So if we're talking about Europeans it's not "I'm half German" as much as "My mother was Swiss-Italian" or, "my surname is Flemish", or "I spent summers in my grandfather's hometown in the Basque Country".

But that's why I brought up colonialism earlier, my impression is that Europeans value integration highly while Americans value ancestry. I've met nonwhite Europeans who got VERY testy at the implication that they were "from" the place their parents or grandparents originated, and considered that way of phrasing it deeply racist. The example of this that always comes to mind is that time Trevor Noah had a fight with the French National football team for saying that the black members of the team were "African", because at the time that argument was popular with the French far right. So in France people thought that saying "this black athlete is African" was a racist thing nazis say to pretend that black people aren't "really" French, while Noah was coming from the colonial perspective of pride in an ongoing heritage that isn't superseded by personal history as much.

So have I met a European who verbalized their white ethnic background as a matter of their own identity rather than the identity of their relatives themselves? Yeeeeah, maybe? But mostly in the context of advocating for seccesionism or just being a nazi, I think.