/usr/lib/x86_64-linux-gnu/libModemManagerQt.so is in libmodemmanagerqt-dev 1.0.1-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libModemManagerQt.so.1
/usr/lib/x86_64-linux-gnu/libModemManagerQt.so.1