And there are patterns for that, that allow you to convert a static exclusivity check into a dynamic exclusivity check - something like a mutex, where multiple threads can simultaneously hold a mutex, but only one thread at a time can gain access to the contents of that mutex. You still enforce that mutation requires exclusive access to an object, but you are now enforcing that at runtime instead of compile time.

You never want multiple threads to be mutating the same data without some form of synchronisation, but with ownership rules, you can still have that synchronisation.