Playbit has keybinding for window management that are designed for it to work as a full OS. But most people trying it today would be running it as a window inside another window manager.
Having an option, or even automatically, rebinding Meta (CMD/Windows Key) to a different modifier when it is running as a window would let keybindings be useful in both the host OS and in Playbit. I think an ALT key is most commonly used for this but it can (mostly) be anything.