How to see all tasks by all staff over all planner boards in one schedule

Are you still looking for the solution?
Because I just solved it! I was looking for the exact thing to have an overall view of the workload for each team member.
What I have done is that I have created a Power Automate flow that creates a List (MS Lists App, which is basically a sharepoint list). The flow automatically at given intervals (say everyday) looks up for all the planners across all teams and channels and the picks up tasks and put them as an item in the List. The fields populated in the List are Task name, Project Name, Status, Due Date, Assigned To and etc. 
And most importantly this List is dynamic and synced up with planners if any changes are made to a task in the planner that will reflect in this List as well (You may have to run the flow or you can set the flow to run every minute).