Lambda function - unknown error

Hello.

Does the same problem occur if you use a different browser or access it from a different PC?
Also, just to be sure, does the IAM user you are using have an IAM policy attached to operate Lambda?
If there is no problem with the IAM policy, please try operating as the root user.
https://docs.aws.amazon.com/signin/latest/userguide/introduction-to-root-user-sign-in-tutorial.html

If the above does not resolve the issue, there may be a problem with your AWS account, 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

It sounds like you've already taken several good troubleshooting steps. Since you’ve tried different browsers, PCs, and even the root user without success, and have already created a support ticket, you’ve covered most of the bases. The next step is to wait for AWS Support to respond to your ticket for a resolution.

Yes, I have tried using a different browser but still face the same issue.

I have also tried using a different PC and am facing the same issue.

I have signed in using the root user.

As you suggested, I have created a support ticket to address this issue. Thanks.