/usr/lib/x86_64-linux-gnu/libReflex.so is in libroot-core-dev 5.34.14-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/root5.34/libReflex.so
/usr/lib/x86_64-linux-gnu/root5.34/libReflex.so