Customer registers an application in the app registration portal (https://app.dev.microsoft.com). He is not able share the application with other users since the “Add Owner” button is missing.
This problem can happen if the user registers the application in the app registration portal (V2 portal) under his personal MSA account. The behavior is documented in the following link:
Re-register the application under an Azure AD account (*.onmicrosoft.com account).