/usr/lib/x86_64-linux-gnu/libBulletSoftBody.so is in libbullet-dev 2.83.6+dfsg-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libBulletSoftBody.so.2.83
/usr/lib/x86_64-linux-gnu/libBulletSoftBody.so.2.83