NewPlanner
Planner: Private tasks now stored in your private plan
Users can now create private tasks in Planner that are stored in a private plan visible only to them. These private tasks cannot be shared or assigned to others, and coexist with existing shared tasks without disruption.
Microsoft's description
Private tasks created in Planner and Planner-powered experiences are stored in the user’s private plan, providing a single place for tasks visible only to that user. Private tasks cannot be shared or assigned to others, and existing tasks continue to work and appear alongside them.