After March 13th, we uploaded IPA packages without a privacy manifest and we still haven't received a warning email from AppStore Connect. So even if we add a privacy manifest, we still can't verify that the privacy manifest we've added in the IPA is correct. Has anyone encountered this situation, is Apple grayscale releasing this feature?
You will receive a warning email after you send the app for Apple approval. It is not enough just to add it to the TestFlight.
I'm testing the status by submitting to app review (with manual release) and then, once I get a warning email I cancel the release. Email is pretty quick. I would say no more than 15-30 minutes.