iPad display brightness adjusting

My iPad 2020 (with fully updated iOS) keeps adjusting the screen brightness. I have automatic appearance (light vs dark) turned off, as well as True Tone off. It happens after the screen locks. For example, when watching a movie, if I walk away and come back, when I unlock the screen, the display brightness is darker even though I set it at full brightness when I was watching the movie. It’s as if the True Tone setting activated even though it’s off. I’ve reset the iPad and am still having the issue. Happens across app developers (e.g., safari and Netflix).

Anyone have thoughts on whether there’s another setting or if this is a known bug?