@joanofark since you have already tried to use a mild abrasive (toothpaste) to eliminate those scratches without success, I think you have exhausted what you can do already. It is possible that these are pressure marks on the LCD. I would suggest to either learn to live with it, or consider replacing the display. That would be a costly thing to do for something that sounds purely cosmetic. I'd say enjoy the functions of the calculator and consider those "scratches" battlemarks of numerical battles.