Created a .desktop file under /usr/share/xsessions as described and
succeeded to log into ctwm but couldn't access any menu whatsoever. I
am using Devuan ASCII. CTWM only has a cross cursor that I can move
with the mouse but nothing else. I tried moving the mouse around
clicking its buttons but nothing happened. To terminate the session I
had to use brute force by pressing Ctrl + Alt + F1 to get to a
terminal, become root and stop slim.