It took a few hours to clean, and at least a dozen big black trash bags.

You got lucky. I once roomed with a hoarder who trashed our apartment that bad too. But if I tried to sweep or dust they’d get really anxious, and if I tried picking things up they’d literally start screaming and shaking. Even piles of old magazines and plastic bags and empty bottles had to stay where they were, let alone heaps of dirty clothes, cheap trinkets, and assorted “stuff”. That person had some bad things happen to them as a kid, and long-term anxiety is no joke.