The C++17 standard says "A program that jumps from a point where a variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has scalar type, class type with a trivial default constructor and a trivial destructor, a cv-qualified version of one of these types, or an array of one of the preceding types and is declared without an initializer (11.6)."

The C++20 standard says "A program that jumps from a point where a variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has vacuous initialization (6.7.3)." and "A variable is said to have vacuous initialization if it is default-initialized and, if it is of class type or a (possibly multi-dimensional) array thereof, that class type has a trivial default constructor."

Note that the C++17 standard mentions a trivial destructor here, but the C++20 standard does not. Now consider this code:

struct MyStruct {
    ~MyStruct() {}
};
void foo() {
    goto x;
    MyStruct s;
x:
    return;
}

It's ill-formed in C++17, but fine in C++20. However, we currently reject this program even with -std=c++20.