Custom WP query ORDER BY with FIELD()

order-by-field.sql

function pn_woocommerce_product_query( WP_Query $wp_query ) {
	if ( $wp_query->get( 'orderby' ) == 'menu_order title' ) {
		$wp_query->set( 'meta_query', [
			'relation' => 'AND',
			'internal_stock' => [
				'key' => '_manage_stock',
				'compare' => 'EXIST',
			],
			'stock_status' => [
				'key' => '_stock_status',
				'compare' => 'EXIST',
			],
			'price' => [
				'key' => '_price',
				'compare' => 'EXISTS',
			],
		] );
		$wp_query->set( 'orderby', [
			'internal_stock' => 'ASC',
			'stock_status' => 'ASC',
			'price' => 'ASC',
		] );
	}
}

add_action( 'woocommerce_product_query', 'pn_woocommerce_product_query' );

function pn_posts_orderby_request( $orderby ) {
	// Output based on pn_woocommerce_product_query()
	if ( $orderby == 'CAST(pn_postmeta.meta_value AS CHAR) ASC, CAST(mt1.meta_value AS CHAR) ASC, CAST(mt2.meta_value AS CHAR) ASC' ) {
		$orderby = "pn_postmeta.meta_value ASC, FIELD (mt1.meta_value, 'instock', '3days', 'outofstock'), mt2.meta_value ASC";
	}

	return $orderby;
}