What’s going on?

Looking for some advice regarding this pepper plant. I’ve had it since it was basically a seedling in early April of this year. I bought it and five other plants, four of which were planted the exact same way and have been beside one another (and this plant until recently) since moving them outside. Four are thriving and then there’s this sickly thing.

Any idea what’s going on with it? I’ve looked closely for pests or other clues without really finding anything. This is supposed to be an Aconcagua, which isn’t supposed to be hot, but figured I would still reach out here for assistance before culling.

EDIT: also worth mentioning that I have applied copper fungicide spray to this plant multiple times without any noticeable effect.