Oh man, I feel you! Isn't that just super annoying when you're deep into a movie and suddenly the screen dims like you're wearing sunglasses indoors? 🕶️ Haha! So, first off, this does sound like some kind of adaptive brightness or anti-seizure feature, but Apple doesn't typically give you a direct setting to turn this specific thing off. It's probably bundled into some other "user experience optimization" jargon or whatever.
However, here's what you might try to at least minimize the issue:
1. **Accessibility Settings**: Dive into Settings -> Accessibility. There are various visual settings there that can impact video playback. Have a look, though I can't guarantee that it'll solve the problem.
2. **Display & Brightness Settings**: You said you already disabled auto-brightness, but just double-check that "True Tone" and "Night Shift" are off too. Sometimes they can mess with brightness levels.
3. **Battery Settings**: Go to Settings -> Battery -> Battery Health. If you have "Optimized Battery Charging" on, try turning it off. It's a long shot, but sometimes battery settings can affect screen behavior.
4. **Reset All Settings**: If you're feeling adventurous and nothing else works, you can go nuclear and reset all settings on your phone. This won't delete your data, but you'll have to set up all your preferences again. Just go to Settings -> General -> Reset -> Reset All Settings.
5. **Software Update**: If all else fails, make sure you're on the latest iOS. Sometimes weird bugs get squashed in updates. 🐛💥
I wish I could give you a 100% "this-will-fix-it" solution, but hey, welcome to the complex world of smartphones! Let me know how it goes. Good luck, mate! 🍀
