https://twitter.com/stephentotilo/status/1762576284817768457/
"NEW: Nintendo is suing the creators of popular Switch emulator Yuzu, saying their tech illegally circumvents Nintendo’s software encryption and facilitates piracy. Seeks damages for alleged violations and a shutdown of the emulator.
Notes 1 million copies of Tears of the Kingdom downloaded prior to game’s release; says Yuzu’s Patreon support doubled during that time. Basically arguing that that is proof that Yuzu’s business model helps piracy flourish."
Some allow you to enable better graphics than the native version, some can downgrade graphics to improve performance. Some remove framerate limits. Some are cheats, with infinite health and similar. It varies a lot, really.
For example, with Tears of the Kingdom on a Steam Deck there are mods to make the game run at 16:10, with better performance, and better frame pacing at 30 FPS. If you’re running it on a PC, there are 60 FPS mods with improved draw distances and shadow resolution.