Sorry to say but that's common with the rock floors, but it could also be they just didn't get enough fall to the drain. it's brand new I'd have them fix it and pick a different floor if you can. Also check the fall on those benches with a level... Since they got the floor wrong. You can use a squeegee to pull the water to the drain until it's fixed.
When I poured my shower pan, I made sure to add a bit of an angle to ensure there’s enough slope. Those youtubers had some examples where in new houses it was all flat. Bunch of crap. Water will puddle there and create mold issues. Have them tear it out and redo
