Currently there isn't really a "window manager" layer. Just like the automation / global hotkeys mentioned above, if you wanted a separate "window manager" your compositor would need to implement a protocol to expose window management. It looks like river is taking a stab at it with their river-window-management-v1 protocol: https://isaacfreund.com/blog/river-window-management/ . If they're successful we might see that protocol adopted by the other compositors.