The "Xbox 360 DLC Archive" often refers to volunteer-led projects aimed at cataloging and preserving content that was never made backward compatible.
: Hundreds of Xbox 360 titles and their associated DLC remain available for purchase and play on Xbox One and Xbox Series X|S consoles through the modern Xbox Store. Xbox 360 Dlc Archive
: This community maintains lists of unarchived DLC , helping preservationists identify exactly which files are still missing from public archives. The "Xbox 360 DLC Archive" often refers to
If you own rare or delisted DLC, you can create your own local archive to safeguard against future server shutdowns: msx360gcdlc directory listing - Internet Archive Xbox 360 Dlc Archive