And if they are to be found there what criteria it, if any uses to determine “with European ancestry” then I'm sure you can produce it, because I searched and couldn't.
And I find that in practice if research include a vague criterion in it's very title, it tends to come with far clearer definitions of that criterion in it's body than this.
I did find it for UK Biobank (one of several sources) earlier, quite easily, by clicking on the relevant link. I suspect that you could not find it (and did not know) only because you don't have relevant training/expertise in science/genetic research - in line with your first question in this thread.
They asked people in the UK in a digitally supported questionnaire/interview, for their ethnicity.
(Wikipedia also mentions that UK Biobank is criticised for sampling bias towards wealthy white Brits)
And I find that in practice if research include a vague criterion in it's very title, it tends to come with far clearer definitions of that criterion in it's body than this.