[mamachan]

thanks to your advice I tried these settings, which go very well:

- Nvidia Shield video settings: 2160p 59,940Hz
- SPMC 16.7.4 video/system settings: 1080p 30Hz (i'm not able to get 60Hz)

In this way:
- all android app (Netflix, Prime video, ecc.....) works in 4K-HDR regulary
- 720p/1080p videos are played at 1080p by SPMC (and upscaled to 4K by TV scaler)

Confirming you get an auto resolution switch (verified by your TV's On Screen Display) downwards from 2160p to 1080p when you play non 4K content with SPMC 16.7.4 ?   

 Yes, my TV's On Screen Display confirm auto resolution switch.
And when i start SPMC i get auto framerate switching on GUI too (from 59,940 to 30Hz). When i close SPMC the system rollback to 59,940Hz