Still, in German, in general, one uses the adjective form, not the noun, to indicate nationality.
Ich bin Amerikaner.
Not
Ich bin ein Amerikaner.
Let’s say, “Ich bin ein Berliner” is somewhat unnatural.
Google translate converts both “I am American” and “I am an American” to “Ich bin Amerikaner.”
Do you dispute these points made in the Smithsonian piece?
“...What is more… ‘Ich bin ein Berliner’ is not only correct but the one and only correct way of expressing in German what the President intended to say,” he wrote.
While it is true that a Berliner is a word for jelly donut, it’s not a term that was used in the area surrounding Berlin, which preferred the word Pfannkucken...”
Bottom line... the jelly doughnut story was fake news. The fact that it’s widely believed does not make it any less fake.