OAuth 2.0 Client Credentials Grant flow is supported for gallery applications - that is, apps listed in the Azure AD Enterprise App Gallery that have custom SCIM integrations built for them. It is not available for custom non-gallery applications using the generic SCIM connector at this time.
Work to add this functionality to the generic SCIM connector is in our backlog, but I don't believe it is targeted for the near future.
There is no location to track this, although the What's New? blog for Azure AD/Entra would be a good place to watch as I imagine it would be announced there.