The source of the picture matters
Apple’s overscan guide documents AirPlay Display Underscan on Apple TV 4K and Apple TV HD for the relevant AirPlay view. It is a source-specific control, not a universal replacement for television picture fitting.
First compare the ordinary Apple TV interface with the AirPlay image. If only the incoming AirPlay picture has the edge problem, preserve that scope rather than changing every input on the television.
Check the documented control
Use the Apple TV AirPlay and Apple Home settings route described for the supported model. Compare the same sender screen before and after the relevant adjustment. Keep TV zoom and source-app crop unchanged during the test.
Use an image with visible corners or interface borders. A film’s intentional black bars do not necessarily indicate underscan or missing content.
Keep normal playback intact
After the AirPlay comparison, check ordinary Apple TV menus and a familiar programme. A useful correction should solve the intended source without creating another picture-fit problem.
For help, report whether the fault affects only AirPlay, all menus or one app. This makes the setting’s purpose clear without claiming it can alter the original source resolution or every application’s external-display behavior.
Questions answered
Is this the same as global television zoom?
No. Apple documents an AirPlay-specific display adjustment.
Should it be used to remove every film’s bars?
No. First establish whether image edges are actually being lost.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.