You can buy a lightning to HDMI adapter or a USB-C to HDMI adapter from Apple (whichever you need) for $30 or so. Then load up the media on the Apple device of your choice, then plug an HDMI between your newly installed adapter and the HDMI in of the infotainment system. Then start the movie on the phone. Should work.
Or, buy a streaming device (Apple TV, FireStick, Roku, etc) and either HotSpot a phone or Subscribe to the Vehicle Data Plan.
GM blew it w/ the Screens. But you have a 2021…which I think was actually the best implementation where at least the screens were more than a Monitor.
So glad I have a COVID era 22, where you could get the Advanced Tech package and not the RSE!!!