Q. How do I get Project and Planner integration capability?

A. To get the integration capability, you need to subscribe to either Project Online Professional or Project Online Premium. For Planner, you need to subscribe to Office 365 Business Essentials, Business Premium, E1-E5, or an Education plan.

https://www.microsoft.com/en-us/microsoft-365/blog/2017/10/30/introducing-new-ways-to-work-in-microsoft-project/