/usr/lib/x86_64-linux-gnu/libConvexDecomposition.so is in libbullet-extras-dev 2.81-rev2613+dfsg2-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libConvexDecomposition.so.2.81