We have released an update to the General Settings section of apps in the Developer Console. Apps created with server side authentication methods (Limited Access, JWT, or Client Credentials Grant) will now show the details of the Service Account user after the app has been authorized. These details include the system generated email address of the Service Account user.
This account is a user representation of the app itself. Apps created with this authentication type default to making API calls as the Service Account user. This new information will help Developers understand that this user was created and provide the details necessary to collaborate files and folders with this user.