There’s two game mode options in the viewport. One in the dropdown arrow which emulates what would happen when you played the game(hides sprites, the gizmo, and uses Post-Process Volume or camera settings). Basically, it allows you to have 2 viewport settings, so in one mode you could have dynamic shadows off for performance and the other with them still on and toggle between the two by pressing ‘G’.
The other, like you’ve found in exposure, works similarly except it’s limited to just exposure. With it checked, it will use the exposure as set by the camera or Post-Process Volume, just like what would happen if you ran the game. With it unchecked, exposure is controlled by the viewport option only just below the checkbox.
With either of those options set to game mode, and your viewport goes black, then you’ve narrowed down your issue to something in your Post-Process Volume or camera.