That's quite inaccurate.

It needs to remain destructible, and if the type satisfies things like (move-)assignable/copyable, those still need to work as well.

For boxed types, it's likely to set them into some null state, in which case dereferencing them might be ill-formed, but it's a state that is valid for those types anyway.

Well it’s unspecified what empty/size return for collections after a move. Not a dereference, not UB but unspecified as I said. UB pops up in hand written code - I’ve seen it and the language doesn’t provide any protection here.

Thankfully clippy lints do exist here to help if you integrate that tooling