Github search gives me 11 300 results for 5000+ stars[0]. Dunno if they all qualify as open source, but that's also repos, not contributors. Presumably there's an average of > 1 per repo.

NPM probably adds a lot. I can't find any recent sources, but NPM packages get downloaded a lot (e.g., every Github Action run.) And to get such a download, an NPM package just has to be somewhere in the dependency tree, which are famously enormous. (Though many might not be updated in the past 3 months, though.)

[0] https://github.com/search?q=stars%3A%3E5000+sort%3Astars&typ...