My MacBook Air screen is fading to black after a few minutes viewing movies

Firstly, it's possible that there's a problem with the display settings or the automatic brightness feature. You can adjust the brightness manually by going to System Preferences > Displays and adjusting the brightness slider. You can also try disabling the automatic brightness feature to see if that resolves the issue.

Another potential cause could be overheating. If your MacBook Air is getting too hot while watching movies, it might automatically dim the screen or shut off to prevent damage. Make sure your MacBook Air is placed on a flat, hard surface to allow for proper airflow and consider using a laptop cooling pad to help dissipate heat.

Additionally, it's worth checking for any software updates for macOS and any updates for the movie playback software you're using. Sometimes, software bugs or compatibility issues can cause display problems.

If adjusting the settings, preventing overheating, and updating software don't resolve the issue, it's possible that there's a hardware problem with the display itself. In this case, I recommend contacting Official Apple Support or visiting Apple Store Online - Apple for further assistance. They'll be able to diagnose the problem and provide options for repair or replacement.