What would be an example of such a software company? I am always faced with this issue with non-software companies in industries where I've worked such as nucl

What would be an example of such a software company? I am always faced with this issue with non-software companies in industries where I've worked such as nuclear, defense, energy, and healthcare. At these places, I've confronted "hands-off" modules that are effectively black boxes of complex logic that has been vetted over decades, is written in C or Fortran, and nobody is allowed to modify. I can't imagine that situation existing in a software company.