not able to select region

It sounds like you may be experiencing an issue with region selection in AWS Device Farm. Device Farm is a unique AWS service that is only available in specific regions, primarily the US West (Oregon) region. Unlike many other AWS services, Device Farm does not allow you to select different regions for testing.

The "global" setting you're seeing and the locked regions are normal for Device Farm. This is because the service provides access to physical and virtual devices for testing, which are located in specific AWS data centers.

If you need to use devices in a particular geographic location for testing purposes, you may want to check the Device Farm documentation or contact AWS support to see if there are any options available for your specific use case. However, generally speaking, the devices and testing infrastructure for Device Farm are centralized and not distributed across multiple regions like other AWS services.

If you're trying to select a region for a different AWS service, make sure you're in the correct console for that service, as region selection behavior varies between different AWS offerings.
Sources
device farm location | AWS re:Post

Hello.

Specifically, which AWS service screen do you have open?
When you open the AWS services screen for global services, the region may be displayed as Global.
https://docs.aws.amazon.com/whitepapers/latest/aws-fault-isolation-boundaries/global-services.html