Consider disabling the High Resolution Textures DLC before you install the game. Those textures can cause problems with the ICE mod, see below, but are also of marginal value on the Deck's smaller screen while almost doubling the size of the installed game (Adds 48GB to the base game's 56GB). Again, do not install the texture pack DLC if you plan to use the ICE mod.
Go into the ... menu while Monster Hunter World is running. Select the Performance tab, then set these values:
Per-game settings: On
Framerate Limit: Unlimited
Refresh Rate: 30
Allow Tearing: On