/usr/lib/x86_64-linux-gnu/libklfbackend.so is in libklatexformula4-dev 4.0.0-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libklfbackend.so.4
/usr/lib/x86_64-linux-gnu/libklfbackend.so.4