I am seeing the same thing on iPhone 12 Pro Max iOS 16.2, would be great to get an update on this issue.

As a work around, I was able to create a new sandbox user by going to App Store Connect -> Users and Access -> Sandbox Testers, I signed out of my current account and logged in with the new one and I can view the manage account page. I did this on an iPhone 12 Pro Max running iOS 16.2