/usr/lib/x86_64-linux-gnu/libsingular-omalloc.so is in libsingular4-dev 1:4.1.0-p3+ds-2build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libsingular-omalloc-0.9.6.so
/usr/lib/x86_64-linux-gnu/libsingular-omalloc-0.9.6.so