Binary package “wmanager” in ubuntu focal

window-manager selection tool used at X startup

 wmanager is a small X11 application for selecting a window manager
 at X startup. wmanager looks for a file named '.wmmanagerrc' in
 the user's home directory which contains a list of window managers;
 you can create such a file with wmanagerrc-update. You can also use
 wmanager-loop that runs window managers chosen by the user until
 told to exit.