You cannot install a mod over an official installation. Back up your save data if you have a legitimate account (though it likely won't transfer).
To build a competitive Extra Deck or a fully powered Blue-Eyes or Dark Magician deck, players either had to spend hundreds of dollars on in-app purchases or grind thousands of duels against the AI. Naturally, this led the community to search for a holy grail: A mod that unlocks every single card instantly. yugioh duel generation mod unlock all cards link
Go to Settings > Security > Enable "Install from unknown sources." You cannot install a mod over an official installation
Most links on YouTube descriptions or sketchy forums lead to dead downloads or malware. The game is abandonware; its development ceased years ago. While you can find working mods on specialized Russian or Vietnamese modding forums (version 1.5.1 specifically), the effort required to avoid viruses is often not worth it. Naturally, this led the community to search for