Hi Kori. This is available today through Project for the web (see the help article: https://support.microsoft.com/en-us/office/move-your-project-from-project-desktop-to-project-for-the-web-143ab391-002e-451a-aedb-3b6fa1f6ab8b). We don't have the import capability in the new Planner app directly, but once you've imported a plan through Project for the web, you should be able to access it through the new Planner app. Thanks.

Hi Kori, this is applicable to premium plans, and today only available in the web at project.microsoft.com. New Plan offers the choice to import a plan and you can choose an mpp. Some limitations apply. https://support.microsoft.com/en-us/office/move-your-project-from-project-desktop-to-project-for-the-web-143ab391-002e-451a-aedb-3b6fa1f6ab8b