Yep, this is what I meant. The "first generation" of these engines were written in COBOL, and are quite nasty by modern standards.

Most people in the tech industry don't apply the ML label to these kinds of software. However, there is a ton of knowledge invested in these systems: certainly more than any one currently-living human has in their head.

A more apt, though out-of-fashion label might be "expert system": https://en.wikipedia.org/wiki/Expert_system