I seem to remember a WWDC session from a few years ago (the one where dyld 3 was first introduced) where they said that dlclose() is now essentially a no-op on macOS, since it’s rarely done, the benefits are few, and the possible problems are many.

Edit: no-op dlclose() was something under consideration for dyld 3 on everything but macOS. https://devstreaming-cdn.apple.com/videos/wwdc/2017/413fmx92...