Microsoft Whiteboard is a standalone service that can't be added as a widget to SharePoint pages. The best that you can probably do is link to a Whiteboard you create via a URL or embed that URL into a page as Whiteboard is available via a browser. The real focus for Whiteboard is to integrate directly with Microsoft teams, since that is the collaboration service of choice these days rather than SharePoint. Whiteboard files can be exported to JPG and SVG once complete and uploaded to SharePoint libraries but for now live Whiteboards live in their own space. However, MS is moving this storage to ODFB if memory serves.