Add a link from the Plan OneNote / files SharePoint site to the Plan itself. (no easy navigation back to the plan at the moment)
When in the OneNote (or files / Sharepoint site) created when adding a new Plan, there is no simple navigation to get back to the plan itself.
For instance, the usual navigation back to the homesite from a OneNote is the title at the top...but this only brings you back from the Plan OneNote to the Plan SharePoint site. Which itself has no direct link back to the Plan itself (the board with the cards).
So browsing back to the plan is impossible - you have to type in the 'Hub' and then click on the plan, and copy the (messy) URL from that Plan, and paste this into the OneNote if you want to make it easy to get back to the Plan from the OneNote. (This seems extremely counter-intuitive to me.)
I always add a back-link manually, but it would be really nice if this were automatic!