DesignPLUS Rich Content Editor tools are not available when working with New Quizzes.
New Quizzes is currently an LTI tool without existing open API calls. As soon as the APIs are available we will begin to research integration with DesignPLUS. We are very interested in integrating with New Quizzes, so we'll make it a priority.
Since the New Quizzes LTI tool creates an assignment in Canvas, our Module Builder has the ability to duplicate a New Quiz as a template just as it is able to do with other assignments but, currently, that is the extent to which we can help with New Quizzes.