Hi @Juan , the main difference here is that AD App Gallery is exclusively for Azure AD. App Source is for the entire Microsoft Suite (Dynamics 365, Office, etc). AD App Gallery's main purpose is to work with Azure AD for things like SSO and user provisioning. There is some overlap, but the 2 different marketplaces make it easier to filter exactly what you're looking for. Please let me know if I can clarify anything or if you have any more questions!
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