A device is considered "vintage" five years after it was last distributed for sale. For vintage products, Apple's retail stores and Apple Authorized Service Providers (AASPs) are still able to offer repairs, but only if the required parts are available.
A device might be shown as "mixed" in Mactracker meaning that some services might be available, but others might not. It's basically an unofficial status between "vintage" and "obsolete".
Take a "mixed" product to two different service shops and you will probably get two different answers about what can and cannot be done as far as service.
For example, if a shop has an old part to fix an iPhone 6 in stock, they will tell the customer that they can fix the phone. If the same customer takes the same phone to a shop that does not have the part in stock....because it is no longer available from Apple.....that shop will tell the customer that parts are no longer available to fix the phone.