Any serious production ruby codebase will have either no monkeypatching, or do it in isolated ways using things like refinements - https://ruby-doc.org/core-3.1.0/Refinement.html

The most I've seen it used is for backporting fixes from future Rails versions or other gems that are hard to update - and again it's easy to do this in an organized and clean way

Just because ruby gives you the tools to do stupid things (and every language lets you do stupid things) doesn't mean that you should do them in a real business app