forcing list input is possible by managing input levels, which can be switched on by clicking on the arrow as in the screenshot and ticking Use Levels option:
From what I have tested, the input levels are managed differently for BHoM and Dynamo (please see ListManagement.dyn from here). Based on my experience, the approach used by Dynamo is quite hard to capture (particularly for the ones grown up on GH trees), but in this case I think it would be fair to say that BHoM should simply mimic the way in which Dynamo handles the inputs (or even better, make Dynamo do that). As an extra reference, you could have a look at the relevant chapter of Dynamo Primer, particularly the List@Level paragraph.
Given that Dynamo is currently not actively supported, it is better to close this issue and open a similar one if this is still an issue with the new version of Dynamo when development is picked up again.
Description:
See comment from @pawelbaran from here: https://github.com/BHoM/Dynamo_Toolkit/pull/267#issuecomment-707095589