> but does it really enforce it

It warns you if you ignore handling a Result because the type is annotated with must_use (which can be a compile error in CI if you choose to enforce 0 warnings). Not that this is true with try/catch - no one forces you to actually do anything with the error.

> What about errors (results) that came from deeper?

Same as with exceptions - either you handle it or propagate it up or ignore it.