Can you tell if the motherboard is actually Lenovo branded, or is it a regular manufacturer like Asus, MSI, Asrock, etc? If it’s one of the later, then there should be a model number on it somewhere, and that is what you’ll want to find a QVL for. Unfortunately even if they use a regular name brand part, there is still a chance it’ll be proprietary to that specific system integrator and not have a published QVL.