I am on Mac OS X, and I use a Magic mouse with it. I'm not sure if scrolling in Simutrans is normally choppy or not, but using a Magic mouse it is. Typically I would use the zoom buttons to zoom around, but theycan be inconvenient. Are there any forthcoming updates to help fix this issue? If a video is needed I can make one to demonstrate what this looks like.
Simutrans only supports certain zoom steps, hence why switching between them will appear choppy.