i made almost all of the world backdrops available in build/buy mode using this tutorial
not included: base game worlds, batuu, and forgotten hollow
things to know:
everything can be found in the 'rocks' category or by searching 'florwalsims'
highly suggest having tool mod to move everything around because once you place them you can't grab them again unless you use it
some of these are wonky and/or incredibly huge!
how to empty a world:
you can do it manually using sims4studio + this tutorial
blowtorch removes most world objects (other than landscaping + backdrops)
awingedllama's willow creek + newcrest emptied