Unhook a closure from a WordPress action by using the class the closure binds to to compare.

unhook_wordpress_closure.php

<?php
/**
 * Unhook a closure from a WordPress action by using the class the closure binds to to compare.
 */

$action_name = 'admin_notices';
$priority = 10;

$expected_class = MyClass::class;

$hooked = (array) $GLOBALS['wp_filter'][$action_name][$priority];

foreach( $hooked as $action ) {

	$function = $action['function'];

	// If it's a string, it's a function.
	if( is_string( $function )) {
		continue;
	}

	// If it's an array then it's an array of [class,function_name].
	if( is_array( $function ) ) {
		continue;
	}

	try {
		$reflection = new ReflectionFunction( $function );

	} catch ( \ReflectionException $e ) {
		continue;
	}

	$bound_to = $reflection->getClosureThis();

	if( $bound_to instanceof $expected_class) {

		remove_action( $action_name, $function, $priority );

	}
}

Nice, @BrianHenryIE , line 38, 'admin_notices' should be replaced with $action_name right?

Yes, thank you. That's updated now.