You will need a dedicated UHD player for the best results with a Dolby Vision display as the Xbox doesn't support that through the disc player, only streaming.
But as far as good looking movies go you should get The Revenant and Blade Runner 2049 as they are regarded as reference quality by a few.
Transformers The Last Knight is another one.
I have been quite pleased with Spiderman Homecoming, Jumanji 2017 and Avengers Infinity War.
I did notice something on the Xbox though. Sometimes the bright highlights won't hit peak brightness unless I change the colour space from limited to full and back to limited in the Xbox settings.
It's probably some kind of hand shaking bug or something.
I might soon buy a Sony X700 UHD player or an Apple TV device. Still researching though as the Apple might be more convenient.
The Sony XF90 is an very nice TV and I am very happy with it.