EDIT:
So according to this thread, this is a Google related change and not Nvidia?
In which case, similar to the banner issue from a previous update, you can get a different launcher (see comments for FLauncher) to avoid it
https://www.reddit.com/r/ShieldAndroidTV/comments/181vh4t/ads_at_full_screen/
Install ProjectIvy from the app store on your Shield or Chromecast with Android TV as an alternative launcher.
Also not buying a Shield anymore in the future. Putting ads in a product you paid for should be fucking illegal at this point.
Would I need to side load this on shield?
These devices are pretty popular, so if you have one it might be time to disable updates
If Google can update the user interface server-side, doesn’t that mean that disabling updates still wouldn’t work for avoiding these full screen ads?
