The error message "An administrator has restricted sign-in" indicates that the account has been intentionally blocked from ...

Running the app through the Command Prompt can bypass the "This App has been Blocked by your System Administrator" message. However, you need administrator privileges to execute the command.

Microsoft has confirmed that users can't open Photos app anymore after a recent Store update for the app. The issue is a result of a non-Admin Group policy or a CSP policy conflict.