I, too, use a Greenworks 60V 21-incher; mine is self-propelled. I mulch 100 percent of the time. I welcome the Turbo mode and use it exclusively, coupled with the optional high-lift blade.
Are you by using the flat, thin, "Economy" blade that came installed? Or heavier, highly swept high-lift blade that came in the box? The heavier blade might force you into turbo mode---at leadt, when the lawn us thick, high, or wet.