Hello @Cobb,Dave,
Yes, you were right. Previously, I was referring to a different gallery application, namely GitHub Enterprise Cloud - Enterprise Account. The GitHub Enterprise Cloud does support SCIM via Entra.
I still have the question... can I add groups to the SCIM solely based on their group name using a scoping filter or any other means?
This is not possible with our service at this time. Mappings and expressions can only be built using attributes contained on the object in question. This means that you can only use attributes on the user object when provisioning a user. Membership of a group is a property of the group object, not the user, and there is no way in our provisioning service to make a mapping that leverages group membership of a user in Azure AD to flow a value in a mapping from source -> target, with the sole exception of the roles attribute via role assignment in the Users and Groups blade of the Enterprise App.