/usr/share/doc/gfortran-multilib-x86-64-linux-gnux32 is in gfortran-multilib-x86-64-linux-gnux32 4:7.3.0-3ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/cpp-x86-64-linux-gnux32