Chosen Solution
The “0=” key won’t backlight on my keyboard all other keys and Touch Bar have normal backlight. sac, nvram reset done without results. No damage received. Noticed after BigSur update, but not sure if it was already like that before the update.
There is a light pipe which directs the light from one of the backlight LED’s. In your case the pipes light path has become blocked. Did you have something spill into the keyboard?
