/usr/lib/x86_64-linux-gnu/libKF5Bookmarks.so is in libkf5bookmarks-dev 5.18.0-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libKF5Bookmarks.so.5
/usr/lib/x86_64-linux-gnu/libKF5Bookmarks.so.5