Doesn’t block *anything*

Check my fix at https://ww.wp.xz.cn/support/topic/critical-security-bypass-on-wp-login-php-due-to-undefined-pagenow-php-8-x/

You can check your status of the variable pagenow with the following two lines:

// DEBUG: Verifica stato variabile pagenow
error_log("DEBUG iQBC: pagenow is " . (isset($GLOBALS['pagenow']) ? "DEFINED: " . $GLOBALS['pagenow'] : "UNDEFINED"));
error_log("DEBUG iQBC: PHP_SELF is " . $_SERVER['PHP_SELF']);