Nvidia shield buffering or not playing on 4k tv

I have a bunch of 1080 films. They stream ok to a 1080 tv via a Roku box. I have a 4k tv with a chrome cast plugged in and it always buffers or immediately stops. It never actually plays.

I want to direct play everything but I cannot disable transcoding. Everything directplayed fine from RPi5. I turn on the button to disable it and it still says transcoding video.

It isn’t actually trying to transcode 1080 to 4k is it?