While not strictly "ISO" (they package games as installers), GOG is the legal alternative. They buy the rights to old games, remove DRM, and repackage them to run on Windows 11. For $5.99, you can buy Diablo or Fallout without the headache of mounting discs.
While many modern games use launchers like Steam , ISOs remain the standard for retro titles and "abandonware." Always prioritize official or well-vetted libraries to avoid malware. Reddit·r/Roms Download Pc Iso Games