Refurbished generally implies used. It's never specified what refurbished is supposed to mean exactly. I don’t think even Apple replaces the battery if it’s still at 99% or so. If it looks and behaves approximately like new, it can count as refurbished. Sometimes it just means adding a box and any missing accessories.Ok, but those are used, not refurbished. If sold as refurbished, it basically is a scam.
People are still using their iPhone X or XS without issues after 6-7 years. LED backlights also degrade with time (though a bit more slowly). LCD screens get dimmer over time, and can shift their whitepoint.Because of the organic nature of OLED matrix. It is starting to degrade the very moment you switched it on the first time, and every subpixel is wearing out at different speeds. I accepted OLED displays as a “necessary evil”, but I’m looking forward to microLED for the future.
Micro-LED isn't coming anytime soon. Not this decade, pretty certainly. And it also has per-subpixel degradation, like all LEDs.