Populating checkbox options with microflow and select/de-select

I am using a microflow to determine the available options in a checkbox and then displaying the options via the simple checkbox set selector.

In the microflow, I create a list of TaskLines. For each TaskLine I set the association back to $DepartmentLine and then on DepartmentLine I set the association to the list of TaskLines.

This results in a list of options available with all of them selected. This is fine for one of my scenarios.

However, for another scenario, I would like to present the same list of options, but nothing should be selected.  I've tried not setting one or other of the associations as above, but then I don't see the list of options.

Can anyone please help me understand how to achieve this?

Thanks,

Tracy