I find some of the sliders for on/off are impossible to read. You can't work out what is on or off.
Windows 3.11 / 95 UI seems such a good idea by comparison to today's UIs - checkboxes with obvious tick marks or X marks in them, radio buttons, buttons that look like actual buttons, scrollbars you can see without having to flail the mouse around just for them to appear, scrollbars that go the right way when you use the mouse wheel (ok that was Windows 98), maximise buttons that actually maximised a window without having to hold alt like on macOS these days...
My dad is colorblind, and the red off/green on looks the same to him; the slight shadow showing the side the toggle is on often isn't dark enough to be obvious, especially when someone gets cute and makes the slider pill-style (the button part takes up exactly half the space, with a vertical line down the middle). I expect this to be less common with mobile OS downtime features that encourage users to get off their screens by going grayscale.
Windows 3.11 / 95 UI seems such a good idea by comparison to today's UIs - checkboxes with obvious tick marks or X marks in them, radio buttons, buttons that look like actual buttons, scrollbars you can see without having to flail the mouse around just for them to appear, scrollbars that go the right way when you use the mouse wheel (ok that was Windows 98), maximise buttons that actually maximised a window without having to hold alt like on macOS these days...