https://www.vox.com/2015/6/1/8689001/seinfeld-fourth-wall

Here's how Jerry's apartment looks if there was a fourth wall instead of a studio audience.

That picture is not of the 4th wall. It's simply an extension of the kitchen wall. The 4th wall would be the wall in the living room that faces Jerry's couch.

Yep. That's just the rest of the Third Wall. They even show a close-up of the kitchen cabinet, which could be seen in many episodes.