Steam downscaling after exiting game

I have set Steam so that it opens in Big Picture mode automatically in windowed-borderless. After selecting a game and then exiting said game, Big Picture mode turns into windowed and is small.

<img width="1279" height="1023" alt="Image" src="https://github.com/user-attachments/assets/359ed4d8-3562-4fda-8e54-a887af0d5888" />