Take a chill pill and wait for a few minutes(hours). It's likely just a bug on Amazon's end. I'm writing this because I couldn't find any other mention of this page when I googled.
While going through this tutorial to create a serverless stack architecture on AWS, I was required to create a Federated Identity through Cognito using the AWS Console GUI on us-east-1.
Having created the Federated Identity, I attempted to access it's Dashboard through the AWS Console but was greeted by a strange error.
When it comes to AWS services not working as intended, 99% of the time it's a User error problem, but this error message was a bit different than normal. I had a Federated Identify on another account on another Region, and I was able to access that one just fine. Something seemed wrong with us-east-1.
I tried changing regions, and then going back to us-east-1 and accessing the Federated Identity Dashboard, and sometimes I was able to access it. But whenever I tried to edit settings, it would kick me back to the above 500 error page.
I tried googling for this specific error, but I couldn't find either 1) a fix or 2) any mention of this specific error page.
It turned out that it just took some time (about an hour for me), but then I was able to access the page as normal. However, diagnosing problems on AWS can be hugely difficult for those like me who are not well versed in it, and that difficulty is compounded when the problem isn't even on your end. So, I felt I should leave some sort of record for the next poor engineer who goes searching for this specific error.
(Of course, this is assuming you DIDN'T have any issues with the settings/code you have written. As always, you should do a sanity check of your services and settings.)
Good luck, and happy coding!