The idea that LEDs last forever is a myth. LEDs degrade over time. They actually list it on the spec sheet. For example an L70 rated led with a 25k hour life will produce 70% of the light it produced when new after 25k hours.

Recently I replaced 4 Asus monitors with led backlights that were produced in 2014 and 2015. Asus says 300 nits. Tested them when I was calibrating their replacements and they were 110-120 at full brightness.

Monitors color shift and dim as they age... that’s why hardware calibrators exist.