We have a gigantic monorepo at work.

To manage the complexity we have entire teams dedicated to aspects of it, and an insanely complex build system that makes use of remote builders and caches. A change to a single python file requires about fifteen seconds of the build system determining it needs to do no work, with all of this caching, and the cache can be invalidated unexpectedly and take twenty minutes instead. Ordinary language features in ides are routinely broken, I assume because of the difficulty of maintaining an index of that stuff on such a huge codebase. Ordinary tools like grep -R or find can only be used with care.