For GCC folks deploying PowerApps for use on mobile platform, on the Login screen for the app, at the bottom right corner, there's a settings gear. You must set your Region for your environment. The default is "Global" and had to set ours to "US Government GCC" for the apps to appear. Took me a while to find this as I was searching PowerApps docs instead of GCC-specific PowerApps docs. As soon as the Region was set correctly, the apps were there. Perhaps this should be in the troubleshooting document?