Xerox’s prototype desktop computer was called Alto, not X, and had some of these features in a very early form. It was never made into a product for the open market; it was used internally at Xerox and at some research universities.
Apple didn’t “steal” from the Alto; Xerox invested in Apple and allowed Steve Jobs and Apple engineers to tour their facilities for product ideas.
You might also be thinking of the X Window System for Unix, whose modern descendant most Linux systems are still using. It’s pretty different from the Mac approach.