After loads of trial and error, using input devices (heck, I even tried the head/camera controls in the accessibility options), I feel like this all comes down to how the mouse/paint tool is refreshing? If that’s even a thing. In simple scenes where there is very little lighting or even better in Unlit mode, the painting & landscape tools are much more responsive and less erratic. I have also noticed that the farther away you are painting something, the more erratic it becomes. That and it seems to coincide with how long I am holding down the mouse button too. For example, if I’m painting, adding foliage, modifying landscapes, etc, if I’m modifying something in the distance, it’s almost impossible to use, but if my camera is right next to it, it’s more manageable. Maybe this all comes down to simply Unreal Engine isn’t meant to be used in a macOS environment (which I hate to say).
I’m not sure if this is simply an Unreal issue either. I also use C4D with Redshift and I’m seeing limitations there too with hardware ray-tracing.