This is where you can use a 'Corona tone mapping control' to exclude your background from being affected by changes you make in the VFB. To see the changes made, you will need to restart the renderer.
Here's an example of how to use it:
Corona light material> In the emission texture slot, drop in a Corona tone mapping control shader. In that, put you HDRI and leave the settings unchecked.
In the VFB, you can adjust your exposure to suit your taste. It may seem like the background is being affected too but it's not, just restart the renderer to see your changes.