Change WooCommerce PayPal Built-in Default Order Status

add_action( 'woocommerce_thankyou', 'change_order_status', 10, 1 );
function change_order_status( $order_id ){
     if( ! $order_id ) return;
     $order = wc_get_order( $order_id );
     if( $order->get_status() == 'processing' )
     $order->update_status( 'pending' );
}