Disable WordPress REST API on WordPress

disable-wp-api.php

<?php
add_filter(
	'rest_authentication_errors',
	function ( $access ) {
		return new WP_Error(
			'rest_disabled',
			__( 'The WordPress REST API has been disabled.' ),
			array(
				'status' => rest_authorization_required_code(),
			)
		);
	}
);