/usr/share/xsessions/mwm.desktop is in mwm 2.3.4-5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | [Desktop Entry]
Name=Motif Window Manager
Comment=Motif Window Manager session
Exec=mwm
TryExec=mwm
Icon=
Type=Application
|