I struggled with this for a long time and even considered redoing my shower to eliminate the glass because it bothered me so much. I tried so many different things, including a lot of the stuff listed here but the best solution I found is barkeepers friend (barkeepersfriend.com/products/soft-cleanser/). It requires zero scrubbing and leaves the glass crystal clear after. I don’t even bother using a squeegee anymore because this is so easy.