AWS region on Console not appearing

This behavior you're experiencing with the AWS Cloud9 environment is expected. When you open a Cloud9 environment, the IDE takes over the full browser window to provide an integrated development environment for writing, running, and debugging code. This is why the region selector and other console navigation elements disappear from view.

To access the region selector or other AWS Console features while working with Cloud9, you have a few options:

1. Open a new browser tab and navigate to the AWS Management Console - this will display the full console interface including the region selector in the top navigation bar.

2. If you need to switch to a different region for your Cloud9 environment, you should do this before opening the environment. In the Cloud9 console's Environments page, use the region selector in the top navigation bar to choose your desired AWS Region, then open your environment.

3. To view environments in different regions, select the appropriate region from the top navigation bar on the Environments page before attempting to open or view your environments.

This is the standard behavior of the Cloud9 IDE interface - it's designed to maximize your workspace for development activities. The region selector and other console navigation elements remain available when you're viewing the Cloud9 Environments page or any other AWS service console page.
Sources
Changing environment settings in AWS Cloud9 - AWS Cloud9
Opening an environment in AWS Cloud9 - AWS Cloud9