A failure to issue a warning is not a refutement of the standard. As I said, yes obviously you can force it. You can force just about anything you want in C/C++.

But if you do

   int& r = *((int*)0);

You'll find it will warn, and tell you that what you're doing is illegal:

<source>:2:14: warning: binding dereferenced null pointer to reference has undefined behavior [-Wnull-dereference]

Same if you try to naively return nullptr on a method that returns a reference:

    int& iref() {
        return nullptr;
    }

<source>: In function 'int& iref()':

<source>:6:12: error: invalid initialization of non-const reference of type 'int&' from an rvalue of type 'std::nullptr_t'

    6 |     return nullptr;

      |            ^~~~~~~

Compiler returned: 1