Scatterbrain
In my case, I merely connect it and it will mirror my screen, media related apps like VLC show a different screen, but will play the video on my TV just fine, but it will not duplicate the movie on my phone itself, which I do prefer.
It is best to keep the phone at a horizontal level for best viewing experience. It is best to use a displayport-compatible cable where one side has a USB-C plug and the other side a HDMI-plug rather than some converter box in between which potentially can cause input lag and other issues.