/usr/lib/x86_64-linux-gnu/libQxtGui.so is in libqxt-dev 0.6.2-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libQxtGui.so.0.6.2
/usr/lib/x86_64-linux-gnu/libQxtGui.so.0.6.2