Planner can no longer be connected to outlook and thus probably no longer to teams as well. Though I am not exactly sure a fan of any of these, connecting Planner was helpful.
We've never used it through Outlook. Only through Teams as a desktop app, as Planner directly in the Office 365 web portal, and by embedding the task board view into our Team group's SharePoint site.
I was just commenting on your conjecture about it potentially not working with Teams. It still does work with Teams.