Mold ?

I’m wondering what’s going on with this nug on my plant. It’s almost done and non of the other nugs look like this. Last photo is the nug right beside it, same plant.

Well that's obviously mold. The spores are all over any plant in the tent by now. You'll start finding more of it.

Might want to salvage what you can and harvest now. Plants might still need some time but they look close enough to harvest before you lose it to mold. You'll have to inspect it well regardless of what you do as the mold doesn't always manifest itself as dramatically as it has with that bud but can still be lurking inside.

Inspect everything and chop anything with mold immediately. Just toss it, it's a loss. Once you've chopped all the moldy buds off (and don't be stingy, get rid of that sh*t) then harvest your plants. I'd take off all the fan leaves and keep the buds in direct breeze while you're drying them to keep any mold spores from growing. I'd dry faster than usual if there was mold. Most of the buds should be okay... you're def close enough to harvest now anyway to go ahead and chop IMHO