In the Desktop app, when there is a due date the icon [due in x days] is shown. Clicking on that allows me to change the due date. When a task needs to be done tomorrow, or it is really due but it has no due date I have to go into the task, select the due button, set a due date.
I would like to suggest in the task overview, to either introduce like the time, energy icons a calender icon to click to set the due date (next to the trash icon?) and/or set/clear the due date from the context menu of the task. This way it is easier to set these dates when none is set.