I have used a good pressure washer [not the cheap low pressure type] to literally "blast" fresh concrete, stucco, drywall "mud" [very easy' and a variety of materials on concrete slabs. driveways, and sidewalks.
IF you get to it quick, it is easier than if you allow the unwanted material to fully, set/dry/cure for hours or days.
If the water pressure is high enough, and the wand is held at the proper angle then, usually, this will work. I have even managed to remove dried exterior paints. Normally, no detergent or cleaners [via the pressure washer] make no difference, so to use them is a waste of material and money.
If the pressure washer is unsuccessful, I have then used an air [pneumatic] tool called a "needle scaler] which will do the job, but care must me exercised to prevent damaging [chipping away] the concrete surface from which you want the stucco removed.