In the Microsoft Graph API documentation it states that it's possible to have application permissions for certain types of resources, even for (personal) Microsoft Accounts, for instance Calendars.Read.
But as it's not possible to receive Admin Consent for personal Microsoft Accounts, (see Graph API - Daemon App with Access to a Personal Microsoft Account (Azure AD V2.0 endpoint))
How can I retrieve the application permissions?
As you mentioned, Application Permissions (aka the Client Credential OAUTH flow) require Admin Consent. Since consent cannot be granted for consumer/personal resources, the Client Credentials flow is not supported for a Microsoft Account (MSA).
From the documentation:
Not all permissions are valid for both Microsoft accounts and work or school accounts.
Any permission (Application or Delegated) that requires Admin Consent would fall into this category.
In order to access an MSA's Calendar, you would need to use the Delegated Calendars.Read permission obtained via the Authorization Code or Implicit OAUTH flows.
