It would be helpful to have it trigger on https://www.wowhead.com/object=419696/waxy-lump like it does for treasure.

Unfortunately I don't know of any ways to scan for in-game objects like that. Historically this would have been great to have for other things, too, so I've looked before.

The only thing in-game that reacts to them is that your tooltip gets set when your mouse goes over them, so you can watch for that... but that's only of limited use given how close that is to you already having noticed it anyway.

I wonder how the game does it for herbs and ore

Blizzard has the advantage of not needing to use the API they give us. Herbs/ore/fish on the minimap are managed from behind the scenes in C code, so it never comes out to a place addons can see.