The game is now tested to be playable on Steam deck. If you are a Steam deck user you may find the following notes useful:
Recommended graphics settings
To get a good frame rate it's recommended to drop the shadow quality to medium and set the scale to 0.75 or smaller. With these settings the game should run somewhat steady 60 FPS most of the time. To make it run better (and to save power) shadows can be disabled and the flora drawing range can be set to a smaller value.
There may be some frame drops under the 60 FPS occasionally because of autosaves or if something big, for example a town, is loaded on the background. The autosave frequency can be adjusted from the settings if the default is too often.
Input
It is recommended to use Steam's own key mapping tool to set your own preferred layout and leave the in-game settings keys as they are by default.
By default there's no Steam deck button assigned for the "discard"-key that is used to discard an inventory item. That functionality is hardly ever needed but can be enabled by assigning a Steam deck button to it manually in the settings.