wp-includes/PHPMailer/PHPMailer.php:4533Check whether the message requires SMTPUTF8 based on what's known so far.
bool public function needsSMTPUTF8() { return $this->UseSMTPUTF8; }Unchanged from 6.9.7 through 7.1.0.
Signature, return type and hooks compared across 3 parsed releases.
src/wp-includes/PHPMailer/PHPMailer.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.