This guide will show you how to mount an ISO file on the Steam Deck. Go through the guide and follow the simple steps to do so.
First, boot up your Steam deck, go to the Discover Store, and search for a mount ISO. After that, install the Mount unmount ISO.
Right-click on the file that you have downloaded, which is live.islroundand, and then select mount/unmount into an image from the pop-up menu. Select mount and it will appear under your Devices list on the left side of the screen.