/usr/lib/x86_64-linux-gnu/libXm.so.3 is in libxm4 2.3.4-13.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libXm.so.4.0.4
/usr/lib/x86_64-linux-gnu/libXm.so.4.0.4