Welcome to Microsoft Q&A and thank you for posting your questions here.
The summary of your questions is to know if there is a "Microsoft Power Platform - AzureAD" equivalent app registration to use for Logic Apps.
On this note I can say: There is no specific app registration for Logic Apps to access Azure AD. However, you can use the Azure AD App Registrations connector to create, update, or delete app registrations in Azure AD from your Logic App. You will need to provide the tenant ID, client ID, and client secret of an app registration that has permissions to manage other app registrations in Azure AD. You can also use the Azure AD Identity and Access connector to perform other operations on Azure AD objects, such as users, groups, or roles.
To achieve integration between Logic Apps and Azure AD, you generally create an Azure AD app registration for the Logic App. This registration grants the Logic App the necessary permissions to access resources protected by Azure AD.
Alternatively, you can use the HTTP action in your Logic App to make REST API calls to Azure AD Graph API or Microsoft Graph API to register an app in Azure AD. You will need to set the authentication type to Managed Identity and provide the audience depending on the API you use.
I hope this is helpful! PS: Do not hesitate to let me know if you have any other questions.
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