At this time HTML5 content is restricted only to authoring presentations and is not available as an option to create a new course in Learning.
If you would like to see this functionality implemented in a future release, please reach out to your Customer Success Manager.
Note: As a possible workaround, you may be able to explore exporting your content as SCORM which can then be used to create a course in Learning. Please consult the support team for the platform used to create your HTML5 content to see whether this is possible.