/usr/lib/x86_64-linux-gnu/libglibmm_generate_extra_defs-2.4.so is in libglibmm-2.4-dev 2.42.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libglibmm_generate_extra_defs-2.4.so.1.3.0