LED Dimming: Time or Use?
According to this article, it is mostly heat over time that causes loss of brightness. And LEDs used for illumination can get really hot.

https://www.digikey.com/en/articles/techzone/2012/feb/understanding-the-cause-of-fading-in-high-brightness-leds

So, if the LEDs are ON, they will age faster. Ambient temperature is still probably warm enough to cause some aging, so they won't last forever at ambient.