It sounds like you're working on embedding a Planner Premium project and roadmap directly into a SharePoint communication site would indeed be a fantastic feature for visualizing timelines and cadences.
Currently, the Planner web part is only available in group-connected Team sites. So, there is no option to embed Planner Premium projects and roadmaps into SharePoint communication site using embed codes.
To get this option in the SharePoint communication site, I recommend submitting a suggestion through the feedback portal. Many features in current products are designed and upgraded based on customer feedback. As more users request this feature, it may be released in the future. Thank you for your understanding and support.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.