How do I add Planner to a Group

My issue was when I created a Group I couldn't find a way to create a plan within it that uses the Planner app. It's possible (in fact likely) that there is a way but it wasn't obvious and I spent quite a while looking.

I've now given up and created a new Team in Teams, I have no problem adding a new Planner plan here. I don't really need the functionality in Teams as this is a (probably) temporary storage location for myself and a (co-located) colleague to use to store documents at the start of our involvement in an existing programme before we have access to their resources. A Group would have sufficed.