PHP Compatibility

I am upgrading our site to PHP 7.4 and it crashes the site when changed. I ran a compatibility scan and it says that there are two files that are not compatible.
wp-content/plugins/login-sidebar-widget/recaptcha/recaptchalib_i_am_not_robot.php
and wp-content/plugins/login-sidebar-widget/recaptcha/recaptchalib.php
What version of PHP is the lastest version of this plugin compatible with? and if it is not 7.4 is there a way to make it compatible with 7.4? thanks.