Steam App ID might be needed to manually access steam screenshot folder on your PC. You will first need to find the ‘remote’ folder inside the Steam directory on your C:\\ drive. If there is a single folder inside the ‘remote’ folder, then you don’t need Steam App ID to access the screenshots.
But if there are too many folders inside it, you can find Steam App ID in a few simple steps. Navigate to the game inside the Steam app. The App ID will be found at the end of the URL at the top of the screen. The URL would look something like this: https://store.steampowered.com/app/240781/