For me, fractional scaling on a HiDPI screen is broken on X11, but works well in Wayland. Here's an example from yesterday: I was playing Factorio full-screen, and some of the GUI elements were too large and wouldn't fit it in the screen. I found a Factorio setting that enabled Wayland, and it instantly fixed the problem. Kudos to Factorio for supporting Wayland! You wouldn't think it was needed for a full screen game, but it was.