You need game files. The most common formats are:
Where to find them? If you own the game legally, use a tool like NXDumpTool on your Switch to extract the ROM to your SD card.
For educational/download purposes: Search for "NSP ROMs" on Internet Archive. Many public domain or homebrew games are available legally. Commercial games are widely available on torrent sites (e.g., "NX Brew"), but we do not link to them here. You need game files
Yuzu is currently the most mature Nintendo Switch emulator available for Android. It has made massive strides in performance, making many triple-A titles (like The Legend of Zelda: Breath of the Wild, Super Mario Odyssey, and Pokémon Scarlet/Violet) playable on high-end smartphones.
You cannot run any game without keys. Legally, you must dump these from your hacked Nintendo Switch using a homebrew app like Lockpick_RCM. Where to find them
This is where your Google search gets dangerous. You want NSP or XCI files.
Risks of "Gratis" ROM sites:
Typical workflow for downloading a Switch game (NSP/XCI):
