What are the constraints on emulating free-hand drawing in Digital media?
The "constraints on emulating free-hand drawing in Digital media" are more about the drawing tool.
An actual pen on paper uses our hand, which can guide it directly on the target surface, with great precision and immediate direct feedback under the pen's point.
A mouse on the other hand means indirection. The mouse is designed for general pointing at UI elements, not for great precision work.
Try an iPad with the Apple Pencil (not a third party one). If you can try with the Apple Pencil 2, and an iPad with a 120Hz refresh rate (aka "Liquid Retina").
Or try a Wacom tablet/artboard and pen as markx2 advised. One with a display if possible (else you still need to get used to indirection).
Both are as close to paper as you can get.
Pen, tablet, lots of controls.