No full screen with my iPad Pro on an external monitor via HDMI

I have 2 iPads and 3 different lightning to HDMI adapters. The HDMI adapter that worked best, was the original Apple lightning HDMI adapter wit a seperate lightning jack for providing USB charging during playing videos.

There are different behaviours of the streams if playing with tennistv.com App or playing via the web site. Tennistv App can only display the 1080p HDMI stream with black borders all around the smaller 16:9 picture on the TV.

Using tennistv.com stream out of the webbrowser without the App the fullscreen command (at the right bottom of the video stream) was actually producing a full sceen display on whatever connected external TV set, with switching the iPads display to a black screen with a central positioned info (in german) „TV angeschlossen. Das Video spielt auf dem TV.“

since a month or so, my iPad Pro 13“ with iOS 16.7.5 refuses to switch to this external mode any more.

My way older iPadAir2-10“ with iOS 15.8.2 is now the only device left, to deliver full screen external stream.

This is definitely no mirroring but external display only.

Why are iOS users not able to use any tool/App to manually define the way how external connected video streams are treated.