Hi,

Just define a new Boolean field called "active" in "sale.order.line" model. In Odoo, this "active" field toggle the visibility of a record.

As per your requirement, if you need to hide the order lines based on condition, you can create a compute function in sale order which fetch all the orderline in the corresponding order and check the len(order.order_line) , if it is greater than 1 , you can just assign active = False for all the lines except the first one

Hope it helps​