The "Update" in the title usually refers to the creator refining the sprites, hitboxes (collision detection), and balancing the characters to feel exactly like the original 1997 game, but often with "boss modes" unlocked, allowing you to play as the normally unplayable boss characters like Orochi or Orochi Iori.
Because these are fan-made projects, they are not hosted on official app stores like Google Play. You can find them on community-led platforms: KOF -97 MUGEN Update Download For Android PC