We are excited to announce that sideloading and custom app capabilities are now available for GCC customers. This is in addition to the third-party app capabilities in GCC that we launched earlier this year, which gave access to hundreds of existing app integrations. With this addition of custom app capability, organizations can now explore new ways to enhance their team's productivity by creating and distributing their own apps on the Microsoft Teams Platform.
These capabilities are disabled by default in GCC environments - admins can enable custom apps through their Teams administration portal:
Once all the related settings are enabled, users in the organization will see UI changes in Microsoft Teams that reflect their ability to directly upload (or sideload) their apps and use them right away. Owners of sites can also control whether the members in their team are enabled to upload apps.
For more details, see the GCC section of the "Distribute your Microsoft Teams app" documentation.