For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Do you have the computer with you ? Because I don’t fully understand your clients message. Is it only external display that’s not working or is it also internal ? If it is only external display problems you need to check everything not board realated first. Such a as try another external display/cable/RIO board/RIO flex and connectors etc.
Also your client talks about a 13-inch machine with onboard Nvidia GPU. It doesn’t make sense as that’s not possible beacuse the 13-inch has no dedicated gpu. That is only the infamous 15-inch that has this.