Unable to start the environment. To retry, refresh the browser or restart by selecting Actions, Restart AWS CloudShell.

Hello.

Try the following.
I have had that error in the past, but in that case I fixed the time setting and it solved the problem.
You can also try changing other browsers.
https://repost.aws/questions/QU0fc_9kRWSF662purgwEacg/questions/QU0fc_9kRWSF662purgwEacg/unable-to-start-the-environment-to-retry-refresh-the-browser-or-restart-by-selecting-actions-restart-aws-cloudshell?

Also, if the problem occurs even after changing the browser etc., it may be an issue on AWS side, so I recommend that you open a case with AWS Support under "Account and billing".
Inquiries under "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html