I am running Ubuntu 19.04 on my laptop and want to use EXWM as my window manager, but am not sure how to get it into the list of window managers that one can pull down when one logs in. It seems to only list "officially supported" ones.
You shouldn't have to. Link or copy the file 'xinitrc' to '~/.xinitrc' and make latter executable by
chmod +x ~/.xinitrc Launch EXWM in a tty1 with
xinit -- vt01
To obtain a tty1 at the login screen just do
ctl-alt <F1>. It's usually
Ctl-alt <F7> to get back, maybe
ctl-alt <F8> depending on your system.
Read docs at https://github.com/ch11ng/exwm On the wiki you will find an example ~/.xinitrc to use as a template.
To get a desktop file to launch from a login window, follow clemera above with
ln -s ~/.xinitrc ~/.xsessions.