Steam Deck

You should definitely use OpenMW instead of vanilla, it's not a mod but is instead a full engine rewrite. It runs natively on linux, has better performance, and a whole lot of other benefits:

• Native support for macOS, Linux, and Windows
• Improved physics and AI
• Distant terrain
• Save/Load dialogs organized by character
• Quality of life UI improvements, such as being able to search for spells
• Multiple quicksaves
• World map adjusts automatically to fit new landmass from mods such as Tamriel Rebuilt
• Support for up to 2147483646 loaded mods (up from 255 in the original Morrowind engine)
• Since it was made from scratch, virtually no engine bugs from the original Morrowind
• And much more

You can install it from the Discover store in desktop mode and then add it to steam, or alternatively you can use a tool like Protonup-qt (also in the discover store) to install Luxtorpeda, which is a tool for automatically launching supported games with rewritten engines. Once Luxtorpeda is installed you can open Morrowind steam properties in game mode, and check the "force specific compatibility tool" box and select to run the game with Luxtorpeda. After that it will automatically run the game through the OpenMW engine instead.