Microsoft Search, Ask Us Anything

At a high level, Microsoft Search indexes the content in M365 and is targeted for "enterprise search". Azure Cognitive Search is for content that is hosted in Azure, and for scenarios that require a deeper level of customization. We do recognize that a lot of customers want the content in Azure to be searched as part of their enterprise search portal, and we have a private preview where you can federated in results from Azure. https://docs.microsoft.com/en-us/microsoftsearch/manage-azure-cognitive-search