When I plug my iPad Pro into my display with Belt HDMI, it doesn’t display the image on the entire screen.Updated a year ago

As of April 2020, this is normal behavior caused by iOS, and does not signify a problem with your cable. Improvements are expected to be made by Apple in future iOS releases. Nevertheless, you can still watch movies in HD resolution with certain iOS apps. 

We suggest you set your iPad in landscape orientation to maximize the size of the image displayed. We also always highly recommend you upgrade your iOS to the latest version to ensure the best performance for your device and its accessories.