PHP 8.0 and 8.1 Error Piwik\mb_strtolower() Doesn’t Exist

Hi, I’m getting the following in my WordPress error logs when I try to visit the Matomo backend (www.mywebsite.com/wp-content/plugins/matomo/app/index.php?idSite=1). Currently running PHP 8.1, but I tried to use 8.0 and had the same result. Everything seemed to be working fine in PHP 7.4 earlier today before updating.

PHP Fatal error:  Uncaught Error: Call to undefined function Piwik\mb_strtolower() in WordPressDirectory/wp-content/plugins/matomo/app/core/Url.php:255
Stack trace:
#0 WordPressDirectory/wp-content/plugins/matomo/app/core/Url.php(315): Piwik\Url::isValidHost()
#1 WordPressDirectory/wp-content/plugins/matomo/app/core/Url.php(397): Piwik\Url::getHost()
#2 WordPressDirectory/wp-content/plugins/matomo/app/core/Url.php(96): Piwik\Url::getCurrentHost()
#3 WordPressDirectory/wp-content/plugins/matomo/app/core/SettingsPiwik.php(194): Piwik\Url::getCurrentUrlWithoutFileName()
#4 WordPressDirectory/wp-content/plugins/matomo/app/core/FrontController.php(395): Piwik\SettingsPiwik::getPiwikUrl()
#5 WordPressDirectory/wp-content/plugins/matomo/app/core/dispatch.php(31): Piwik\FrontController->init()
#6 WordPressDirectory/wp-content/plugins/matomo/app/index.php(25): require_once('...')
#7 {main}
  thrown in WordPressDirectory/wp-content/plugins/matomo/app/core/Url.php on line 255