Windows 3.11
Maybe Microsoft should have stopped with Windows 3.11? My biggest complaint with Windows, apart from the primitive UI, is whenever a new version is released, you have to jump through hoops to switch things off. Also, sometimes things just appear for no reason, for example the diagonal blue arrows to indicate a compressed file. There was already an option in file explorer to indicate a compress file, which you could turn on or off with a check box. The blue arrows required hacking the registry.