The app version of Microsoft Planner as found within Microsoft Teams is optimized for collaborative efforts. While the web version of Planner has some functionality outside of Teams, it currently does not synchronize across platforms.
If you are sharing your Planner with others in Teams, we encourage you to use only the version of Planner within Teams to coordinate tasks within channels. If you need functionality from the web version of Planner, select Go to website option.
This redirects you to an online version (tasks.office.com) that will synchronize with Teams. Using the Go to website option will grant you access to Boards and Charts. The instruction above is a temporary workaround. We are currently developing a future update that will resolve the lack of synch functionality.