I am playing on Steam deck and it works out of the box (at least the Steam version). However, Wurm unlimited require you to disable GLSL from settings (otherwise it will crash).
Here is my settings what I using. With these settings deck uses around 12watts (+2 hours when on battery).
In-game: medium settings, far view distance.
Deck: 40fps lock and 40hz refresh rate. 8 TDP cpu and 800mhz gpu.
While you are doing bricks change fps lock from 40 to 10. With this you can play on battery +6 hours.
There is a really good community made layout "Wurm Online Steam Deck V11" by Tobe.
EDIT: Forgot to mention that I am using CryoByte33/steam-deck-utilities mod to increase my swap file + chaning swapiness. Here is good video about this mod