The variables property of the https://purl.imsglobal.org/spec/lti-platform-configuration claim in the response to a request for the platform registration only contains the standard capabilities and omits any variables defined by resources declared by LTI services (for example, LineItem.url).  I think this list should include all variables supported by Moodle, and hence include those handled by any supported LTI services.

To reproduced the issue, navigate to the mod/lti/openid-configuration.php page of a Moodle site and inspect the variables element returned in the JSON.  Variables such as LineItem.url are missing.