Hello nea130,
Thanks for that info and for choosing the Apple Support Communities. If we understand correctly, you are unable to play videos on your MacBook Air as expected. To help isolate this, use safe mode to start up your Mac as it does the following things:
- Verifies your startup disk and attempts to repair directory issues, if needed
- Loads only required kernel extensions
- Prevents Startup Items and Login Items from opening automatically
- Disables user-installed fonts
- Deletes font caches, kernel cache, and other system cache files
Log in to your user account and test the issue while in safe mode and then restart normally and test the issue again.
How to use safe mode on your Mac
Graphics performance limited in macOS Recovery, safe mode, or Guest User mode
Cheers!