In Ruida it’s throwing away 3/4 of your source file when you do that, in LightBurn it doesn’t let you because if you pre-dither I assume you want all of it.
With a 90w laser, your beam spot is going to be about 0.16mm or larger, so there’s no point in dithering at 600 DPI - the lines will overlap badly and ruin the shading. Newsprint or Halftone will give you good results at that DPI because they’re designed to reduce overlap.