Looks to me like something is scorching the wall. Could have been something inside the cabinet, like putting away a cast iron pan while it’s still hot, but my guess is you have a screw in the wall there that is screwed into a shorted electrical cable.

I could definitely be wrong, but I’d cut a hole and see what’s back there anyway.

I agree about cutting away the drywall. Easy to fix after, especially since inside a cupboard. I would avoid touching with metal and wear insulated gloves I think.

It’s an IKEA cabinet with a melamine backing. I’m going to pull the micro and cabinet out and we’ll see what that shows us

That it’s melamine changes my thinking. Looks like a hot nail but guess it’s not.
Gonna change my mind to stain or burn.

Holy shit

Hoo boy you must be insanely glad you caught this when you did.