They don't really mean anything on desktop anymore seen as only a small minority of MacOS apps are built using those frameworks. Everything else is either Electron or custom cross platform UI frameworks like Adobe Suite, Alberton, Cinema4D etc.

The HIG is just as applicable if you use Electron, even it might take more work to follow the guidelines if you don't use the system-provided widgets.

That some choose to ignore the HIG and use the same GUI on multiple platforms is a problem, but it's not a problem that any guidelines can solve.