Can not delete stack even I am root user

Hello.

You need the IAM role indicated in the error message, but the error may have occurred because it has already been deleted in the failed delete process of the stack you are trying to delete.
So, creating an IAM role with the same name may solve the problem.
I have solved similar errors this way in the past.
https://repost.aws/questions/QUazDA4tWPSLOb9Z1Ikxe2CQ/i-manually-deleted-a-specific-resource-and-i-can-not-delete-the-cloudformation-stack#ANBRAsNu-0QFG59UywJn7jvg