/usr/lib/x86_64-linux-gnu/libKF5MessageComposer.so.5abi2 is in libkf5messagecomposer5abi2 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/libKF5MessageComposer.so.5.7.3.abi2