Although it might sound a good idea to use Github Gists for certain cases, but in general it does not!

Simply, because gists lack of security (might expose sensitive data, even if it's a secret gist, still can be accessed by the link), not made to handle huge traffic at once, doesn't track users to show how many users are accessing it and when..

On the other hand, you've got Firebase Remote Config which can handle high volumes of requests efficiently, offers built-in security features, such as encrypted communication, authentication, and role-based access control. You can manage configurations safely without exposing them publicly, can be integrated with Firebase Analytics, allowing you to create custom configurations and target specific user segments, and more...

Also it allows you to add JSON as well, so I would highly recommend using FRC rather than the Github Gists for most cases.