I need to correct myself. Blacks are not raised in the TV+ app. I know they were, but maybe that was with the 09 firmware and I hadn’t checked .16. Sorry about that.
I would have thought the internal app would be free from raised blacks, everything I have read says the internal apps are fine now, no-one actually mentioned the apple tv app though.
I take it you are on the latest 3.21.16?
Somewhat ironically it makes the Apple TV 4K the worst way to watch Apples own content.
A Firestick is fine, the TV app is fine, the ATV......errrr! Embarrassing really.