Kindly reach out to the Store/Individual/Agency from whom you acquired your iPhone 11. They would be best equipped to confirm whether the device has undergone servicing by an unauthorized service provider.
In case you recall not encountering this message at the time of purchase and it surfaced after an update, it's important to note that this message is visible specifically on iOS 15.2 and subsequent versions. It might be beneficial to inquire about any recent updates or changes made to the device's software configuration that could have triggered this notification.
Understanding the circumstances surrounding the appearance of this message could provide insights into any alterations in the device's service history or software updates that have brought about this notice.

Parts and service history
With iPhone 11 models and later, excluding iPhone SE (2nd and 3rd generation), using iOS 15.2 and later, you can go to Settings > General > About for the parts and service history of your iPhone. You can also find out if the display has been replaced. If the repair was done using genuine Apple parts and processes, "Genuine Apple Part" will appear next to Display.


- An Unknown Part
message will appear if the display installation is incomplete or if the display: - Was replaced with a nongenuine display
- Was already used or installed in another iPhone
- Isn't functioning as expected
An additional message might appear that says "Apple has updated the device information for this iPhone." This means that Apple has updated the device information maintained for this iPhone for service needs, safety analysis, and to improve future products.
These messages don't affect your ability to use your iPhone.
Learn more about iPhone parts and service history.

The only way to get the notification removed is by replacing the ingenuie parts with a genuine Apple Parts through an Apple Authorised Sercvice Center.

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:
Apple Repair and Repair Status Check - Official Apple Support
Apple Authorized Service Provider
Find Locations - Location Selector - Apple
Contact Apple for support and service - Apple Support