I cannot mirror image my iPad onto tv with Apple TV 4K

Please review this support document on all the needed steps.

Use AirPlay to stream video or mirror your device’s screen - Apple Support

and

If AirPlay or screen mirroring isn’t working on your device - Apple Support

Some content can’t be mirrored (i.e. doesn’t allow it to be mirrored) at the content provider’s discretion.

If you can mirror the iPad Home Screen, then AirPlay Screen Mirroring itself is working correctly.