As of now, Microsoft Graph does not support filtering on schema extension properties directly when querying resources like contacts. Schema extensions are custom properties added to resources, but Microsoft Graph does not provide full support for filtering based on those properties in its OData $filter queries.

While you can retrieve schema extension properties using Graph API (by including them in the $select clause), filtering based on them is not directly supported via $filter. You would typically need to retrieve the contacts first and then filter them on the client side.