Not in that exact fashion (can you set another style as default? white and black 1px would not be my choice for many/most designs).
Workarounds in Vectornator:
you can keep e.g. a little “default” object in a corner/somewhere and just click on that before creating a new shapes, or
you can use Copy Style from a “default” object and Paste Style (on selected objects). Note: for groups and similar. you might have to select the objects in the group, not the group itself.
Using a default object is not really a solution. What if you have a dozen artboards? You now have to keep a copy of that default object in every artboard. Or worse, go hunting for it whenever you need it. Not even close to just pressing D.