There are many unclear things in the GDPR, but the relevance of citizenship is not among them: Nothing in the text of the GDPR or any official guidance mentions

There are many unclear things in the GDPR, but the relevance of citizenship is not among them: Nothing in the text of the GDPR or any official guidance mentions citizenship or nationality. The only sources which do mention those are informal and imprecise third-party summaries. But yes, this mistake has been spread widely. The more precise compliance guides from, say, European law firms don't mention citizenship or nationality either.