/usr/lib/x86_64-linux-gnu/libKF5MessageViewer.so.5abi4 is in libkf5messageviewer5abi4 4:17.12.3-0ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libKF5MessageViewer.so.5.7.3.abi4