Linux

I won't bother going into technical details about x11 and wayland since other people already explained it much better than i ever could, but basically wayland is supposed to be replacing x11, because the codebase is so old now that it has become very hard to maintain and implement new features without breaking things. A window manager pretty much only handles the placement of windows on the screen, and you have to use seperate applications for setting a wallpaper, getting notifications, application launcher, etc. Whereas a desktop environment is a fully fledged out of the box experience. I personally really like window managers because i like the workflow of tiling window managers in particular, which places the windows in a predefined layout for you. Something that might be a bit confusing is that window managers on wayland are called compositors, which is because in wayland the window manager also has to do it's own compositing. In x11 you could use something like picom, which is a seperate compositor program that you could use to add graphical effects to any window manager, but on wayland this doesn't exist and the window manager has to implement its own compositing.