iPhone 13 Pro Max OEM screen replacement error message "unknown part"

Only Apple or Apple Authorized Service Providers have access to Original Authentic Parts. I suspect whoever you used to do the repair may have misled you to believe they were installing an OEM screen, but I highly doubt this "independent" service would actually be able to install OEM parts.

Regardless, you'll have to take the back to them. And if the part is not OEM as it likely is not, the unknown part message will not go away. And Apple will unlikely be willing to service a phone which has been tampered with by anyone other than Apple or an actual Apple Authorized Service Provider. For example, in the US, BestBuy is an Authorized Service Provider. And there are hardly any others out there.

You didn't roll back to the original operating system if you were running iOS 16.1 and a build number ending with a letter. You need to roll back to iOS 16.0.2 for the configuration software to properly function.

Hello, JrsKjs.

Let's start out by taking a look at this support article which may help explain this message you are seeing: iPhone parts and service history - Apple Support. The article explains:

"An Unknown Part  message appears if the part installation is incomplete or if the part: 

• Was replaced with a nongenuine part
• Was already used or installed in another iPhone
• Isn't functioning as expected"

Please also note this section:

"Importance of service by trained technicians using genuine Apple parts

For most customers, visiting a professional repair provider with certified technicians who use genuine Apple parts is the safest and most reliable way to get a repair. These providers include Apple and Apple Authorized Service Providers, and Independent Repair Providers, who have access to genuine Apple parts.* Repairs performed by untrained individuals using nongenuine parts might affect the safety and functionality of the device. Genuine Apple parts are designed to fit precisely within the device. Additionally, repairs that don't properly replace screws or cowlings might leave behind loose parts that could damage the battery, cause overheating, or result in injury.

Depending on your location, you can get your iPhone serviced — in or out of warranty — by visiting an Apple Store or Apple Authorized Service Provider, or by shipping your iPhone to an Apple Repair Center. Genuine Apple parts are also available for out-of-warranty repairs from Independent Repair Providers or through Self Service Repair."

Let us know if we can help with anything else at all or if this doesn't settle your issue so we can look into this further with you. Thanks and have a fabulous day!

Those are some typed words and may be as valuable as the paper they are typed on. You need to take this up with the service provider. At this point it's between you and them.