@gthief
Thank you for reporting that auto-brightness is not functioning while playing the app.
Please make sure that auto-brightness is off just in case.
To turn auto-brightness on or off:
In the Settings app, tap Accessibility. Tap Display & Text Size. Scroll to Auto-Brightness and tap to turn the feature on or off
If this does not resolve the issue, please let us know the following information so that we can investigate further.
Screenshot where we can confirm that auto-brightness is off