by kaggdesign on WordPress.org
WordPress is not fully compatible with PHP 8.0 – 8.4. Remaining known PHP 8.0+ issues are deprecation notices.
The same is related to many popular plugins such as WooCommerce, Jetpack, Gravity Forms and others. Mainly, they produce deprecation notices from the Action Scheduler library.
kagg-compatibility-error-handler.php into the /wp-content/mu-plugins/ folder. It contains the error handler, which loads earlier than any plugin or theme.