Had the same problem in 4.20, Luckily you can always press “no” when App Store Connect asks the question. But if you still get the red warning with the text:
“Your app is using the Advertising Identifiar (IDFA). You must either provide details about the IDFA usage or remove it from the app and submit your binary again.”
You can press “yes”, Check the first option. Then press “no” again and then submit.
That made it send it away to the review for me. Still dont know if they’ll approve it. I’ll be back when I know.
(This seems like a obvious bug tho)