Remove filters added from class instances on a specific hook.

Remove Class Filters Example

class Test_Class {
	
	public function __construct() {
		add_filter( 'pre_get_posts', [$this, 'test_callback'] );
	}

	public function test_callback() {
		wp_die( 'Hooked up.' );
	}
}

$test = new Test_Class();

add_action( 'init', function () {
	remove_class_filter( 'pre_get_posts', 'Test_Class', 'test_callback' );
}, 99 );

remove_class_filters.php

/**
 * Removes a filter added from a class instance from a specified hook.
 *
 * @param string  $hook             The filter hook from which to remove the callback method.
 * @param string  $class_name       The name of the class containing the method to remove.
 * @param string  $method_to_remove The name of the method to be removed.
 * @param integer $priority         Optional. The priority of the function. Default 10.
 * @return bool Whether the function existed before it was removed.
 */
function remove_class_filter( $hook, $class_name, $method_to_remove, $priority = 10 ) { 
	global $wp_filter; 

	// Bail early if there are no callbacks on this filter.
	if ( ! has_filter( $hook ) ) {
		return false; 
	}
	
	$callbacks = &$wp_filter[ $hook ]->callbacks;
	 
	// Exit if there aren't any callbacks for specified priority 
	if ( ! isset( $callbacks[ $priority ] ) || empty( $callbacks[ $priority ] ) ) {
		return false; 
	}
	
	// Loop through each filter for the specified priority, looking for our class & method 
	foreach ( $callbacks[ $priority ] as $callback ) { 
		// If the callback is not an array, skip it.
		if ( ! is_array( $callback[ 'function' ] ) ) {
			continue; 
		}

		// If the callback matches the class and method we're looking for, remove it.
		if (
			$callback[ 'function' ][0] instanceof $class_name && 
			$callback[ 'function' ][1] === $method_to_remove 
		) {
			return remove_filter( $hook, array( $callback[ 'function' ][0], $callback[ 'function' ][1] ), $priority );
		}
	} 

	// We only get here if no filter was found.
	return false; 
}

This is an example of a helper function that can be used to remove a filter that was added by a class instance that is not accessible along with a simplified test case to show how this would apply.