Is 4K streaming available on Google TV?

I love streaming Nebula on my PC at 2160p quality. I've recently bought a Xiaomi TV Box S (3rd Gen) that runs Google TV. I've noticed that the Nebula app on the platform doesn't have the option to choose a resolution for each video and the resolution doesn't seem to reach 4K. Am I missing something or is 4K simply not available through the Google TV Nebula app?