I know what’s going on there, Shield TV isn’t in true 4k mode even though you have those settings activated.
If your home screen looks like this:
Then it’s being scaled down to 1080p still.
For true 4k mode go to settings/device preferences/developer options then look for this setting:
After turning that on reset the Shield then your home screen should be in true 4k mode like this:
Just to let you know though that the Shield simply isn’t powerful enough to run the 4k presets, here I am getting 24fps:
And this is on a overclocked Shield with cpu, gpu, ram maxed out in performance mode, still struggling. You’re better off just using the 1080p ones on Shield.