The Esc key can be used to quit every interface except for when you talk to a shop owner. Pressing Esc while in the shop vendor scene causes the game to enter the "Pause" menu, and you can only use the mouse to select "Goodbye" to exit the shopping interface. I think it would be a good QOL improvement as I keep mistakenly pressing the Esc key and it pauses my game when I try to exit the shopping scene.

The referenced scene is whenever you interact with the shop owner's menu and it opens up the options
"1. Purchase 2. Sell 3. Goodbye"