After downloading Vassal on my Windows 11 laptop, when I download a module it opens in vlc media as a photo.
It sounds like you’re double-clicking a module file and the wrong program is associated with the file type. Here’s one of umpteen guides on the internet about changing default applications and managing file associations generally.
To reliably get a module open in the meantime while you figure that out:
- Launch VASSAL first
- File menu → Open module
- Navigate to where your module is stored and select it.