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)