/usr/lib/libpanel-applet-4.so is in libpanel-applet-4-dev 3.8.1-7+b1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libpanel-applet-4.so.0.1.1
/usr/lib/libpanel-applet-4.so.0.1.1