Peugeot 508 Brake Light Error

Could be a faulty switch, but those usually just fail outright. Did you check the bulbs themselves? Sometimes a bad bulb can throw a code. Also, any recent work done on the car's electrical system?

Bulbs are fine. Nothing done recently, just normal driving. If it was the switch, would it just be a straight replacement or is there some coding involved?

Given it's a 2019, it probably needs coding to the car's computer. If it was my car, I would take it to a workshop to get it checked out.

Turns out, after taking it to a workshop, I had inadvertently triggered the cruise control's brake override function somehow. The mechanic reset the system, and everything is back to normal. No cost to me.