when i try to stream a movie from my library to apple tv on may macbook 2020, i can only hear audio but shows a black screen
What is your model Apple TV? Identify your Apple TV model - Apple Support
From which content provider are you trying to stream, and from which application? Some content may be unsupported or blocked for AirPlay. Can you mirror the desktop? Then AirPlay mirroring is functional.
Use AirPlay to stream video or mirror your device’s screen - Apple Support
If AirPlay or screen mirroring isn’t working on your device - Apple Support