Joe's answer is smart, but for some reason I couldn't use that. Instead, I did this and the warnings disappeared from the Apache error log.

At the very end of wp-config.php, add:

error_reporting(E_ALL & ~E_WARNING & ~E_NOTICE & ~E_DEPRECATED & ~E_STRICT);

Tested on: FPM 8.0 / WP 6.8.2