How to see multiple Plans at the same time?
While there is currently no simple way to view all Plans at once on the same Dashboard, a possible workaround would be to try out the Teams view.
In Plan, you can assign each task to a user. Whenever you assign a task to a user, you can see this same task assigned to the user in the Teams view. To switch between Plan and Team timeline, click on the name of the Plan on the Team timeline in Sidebar.
If you go through your each of your projects and assign all of the tasks to users, then when you switch to Teams view, you will see all of the tasks on the timeline beside each user's name. At the moment, this is the only way to link the two together; all tasks need to be assigned a user so that they will appear in Team timeline.