Unfortunately I do not think it is this simple because we keep a singleton of this cache and then re-expose its methods at the module level.

I think the steps here are:

• keep the load function private
• write top-level functions that replace find_font and get_font_names (minor API break but we need it to make sure if someone does from matplotlib.font_manager import find_font and then we update the cache the function they are holding onto is not the old one...I guess we could fake the method properties on a function but it is not worth it)
• write a new top level function like reload_fontcache or something similar name that updates the fontManager singleton. If someone has done from matplotlib.font_manager import fontManager I think we are stuck in a world where they will still have a reference to the old one! I guess we could deprecate it as a publicly accessible

An alternate path would be to update FontManager to be able to have its internal state updated.

An alternate to my last comment is to explain why this does work as it looks like it creates a new FontManger that we then throw away, but some how the existing FontManager is changed?

Haven't read through the whole issue, but note that in the rebuild_if_missing branch at the end of findfont_cached, fontManager calls _load_fontmanager then replaces its __dict__ with the contents of the newly loaded instance (so the old one really becomes a copy of the new one).

See also #13810/#13852, which may be worth revisiting?

That is a bit heavy handed, but makes sense (a recache method might be better).

However the way this is hidden behind a cache, we will only automatically discover the new font if it is there when we search for it. It might be worth also adding a public way to clear that cache.