There are several things you can try and test to see which one suits you the best such as the specific iPad model, the game's graphics settings, and other factors. First of all, Genshin Impact requires iPadOS 9.0 or later, so make sure you're running the latest or atleast minimum required version of iPad. Second, make sure that the game is updated to the latest version. Next, reduce the graphics settings within the game. Finally, close any other apps running in the background while playing Genshin Impact. Lastly, Restart the iPad.