Viewport response when painting is done by graphic card. Deepending on its specs it can be lagging, or even become unresponsive. Downgrading OpenGL display can help (either globally from Options, on a per viewport basis, or on an ecosystem species basis)

If you have plants on tree tops, it's because you didn't check what object to paint. By not doing so, it paints everywhere the mouse is passed.

I recommend reading your Vue manual.