Downloading XCI files (a format used for Switch game backups) for free from the internet is not recommended. Not only can this be illegal, but it also poses risks to your device (like the potential for malware) and your Nintendo account (risk of being banned).
Alternatively, some PC-based emulators like or Ryujinx can load XCI files to play Switch games on a computer. Pokemon Legends- Arceus Switch XCI Download gratis
