Is it possible to make a task visible to all members of a workspace?
A task can only be visible to the members of the list it belongs to. It's not possible to make the task visible to the entire workspace.
If you want a task to be visible to all members of the workspace, you should create a list and add all your members to that list. Then, all tasks within that list will be available to them.
Tasks in this list with a due date will appear on the calendar/schedule view and will be visible to others as well.