I always wonder how can one come to such a conclusion. Modern C++ has no way to enforce relationship between two objects in memory and the shared xor mutable rule, which means it can't even do the basic checks that are the foundation of Rust's safety features.

Of course, this statement is also trivially debunked by the reality of any major C++ program with complexity and attack surface of something like a browser. Modern C++ certainly didn't save Chrome from CVEs. They ban a bunch of C++ features, enforce the rule of two, and do a bunch of hardening and fuzzing on top of it and they still don't get spared from safety issues.