I have used CLR to dissolve hard water stains and build up on plumbing fixtures, kettles, etc. Also use on shower glass doors.
Water is very hard here so we have a water softener unit also.
Try in a small spot first of course. And of course in future use that chamois to get the windows dry after washing.
https://clrbrands.com/Products/CLR-H...d-Rust-Remover

Jim