one quick fix that I used is modifying the dropdown file from Template/task
#<?= $task['reference'] ?>
I replaced the ID task with the reference number since this is important for the user. But this only affects the Board and list view.
Later edit:
I managed to remove de ID also from the calendar view: I rmodified the TaskCalendarFormatter :
‘title’ => t(’#%d’, $task[‘reference’]).’ '.$task[‘title’],