I actually use DEMto3D. It's touchy, but I do post-work on the .stl/3d model in blender so it works out ok for me.

If you have weird artifacts, I'm guessing that is due to the underlying data vs QGIS itself. Have you looked at their documentation (https://demto3d.com/en/)?

I outline how the whole process works here https://www.gregkamradt.com/gregkamradt/2020/2/29/manufactur...