Why am not able to sidelong apps not found in app store?

I tried to install downloder from the play store. After downloading app and opening it the browsers says this app is restricted on this device. This Nvidia Shield is the older version I use in living room my Nvidia Shield in bedroom does the same (the page you are trying to access is restricted) but I have a fire TV box which allows me to sidelong with no problems. Also did turn on allow unknown apps to install.

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