"In Train Sim World 5 Photo Mode, I can’t use my mouse to move the sliders for adjustments (like brightness, contrast, etc.). The arrow keys work for moving the camera, but I can’t control the sliders with my mouse. Does anyone know a fix for this?"
Click the number you want to change and use the Arrow, the activation zone for the sliders is small, so it does get a bit finicky, more often I use the arrow keys once I click the number I want to change.
My error, my apologies, as soon as I get into the game I will check my game. Have you tried to validate the game, some times the updates get messy and something is missed or corrupted, Steam will require the needed files if need be.
Try doing the Game validation again. I was able to use the sliders, still very Finicky and has a small, tiny activation zone. In-Game Photo Mode Via Steam, my apologies for the multiple images, there was no other way to show the in-game sliders.