Sorry for my late reply. It has something to do with the security settings as your log contains the following error:
Read access denied for member 'System.UserRoles' of object 'Administration.Account'
Could you go to your App Module > Security > User roles > Open the Administrator User Role > Check the 'User management' settings at the bottom of the modal. My guess is that your settings there aren't configured correctly.
Is there by any chance another error in the log? If not, have you tried debugging the Microflow that is triggered when creating a new user? This shows you which action leads to the error you're facing.