Can the ES2020 nullish coalescing operator (??) be used to check undeclared variables?

Question

From MDN:

The nullish coalescing operator (??) is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.

However, the following statement doesn't seem to work if the variable isn't declared:

console.log(foobar ?? 555);
// Uncaught ReferenceError: foobar is not defined

If I explicitly declare the variable, it works:

let foobar;
console.log(foobar ?? 555);
// 555

The only alternative appears to be:

console.log(typeof foobar !== 'undefined' ? foobar : 555)
// 555

Is there a cleaner way to check if something is undeclared and return a fallback value?

I know there's an argument against why code would check for a variable that wouldn't be declared. For example, the following function accepts a parameter without assigning it a default value, making ?? seem useful:

const baz = (foobar) => (`${foobar ?? 555}baz`) // same as: const baz = (foobar = 555) => (`${foobar}baz`);
baz()
// 555baz

Is this scenario the intended use of this operator? If it is, then also be served by assigning the argument a default value in the signature, so how does the nullish coalescing operator differ itself in usefulness?

Note: The statements above were run in Node.js 14 as well as Chrome 88.