This is simply false and an oft repeated myth. Undefined behavior has a specific technical definition that is in the C++ standard [1] and there is absolutely no mention in that definition or the implication of that definition that undefined behavior necessarily results in an invalid or incorrect program.
The definition of undefined behavior, right from the standard itself is... and I quote... get ready for it...
"behavior for which this document imposes no requirements"
That's it, nothing more, nothing less.
The standard even goes out of its way to state the following:
"Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, *to behaving during translation or program execution in a documented manner* characteristic of the environment".
Behaving in a documented manner characteristic of an environment is a far cry from being by incorrect by definition.
[1] https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/n49...