As far as I know it is the only Disgaea game that runs on the Steam Deck at the moment. (Hasn't tried any of the other but they are all listed as they are not functioning or hasn't been tested.)

You do need to do following settings:

In the settings for the game in Steam Deck you must change the D-pad so up is down and down is up. Then you need to do this under Gamepad Configuration inside the game as well. Otherwise they will be the opposite direction (have no clue why).
For Screen Size chose "Fullscreen A", for Resolution go for "Default" and not "1280x800", this settings will give you the smallest black borders.

There are some graphical glitches, in the main hub/village, Adell can walk through buildings. A bigger issue is that in some levels enemies are visual through objects so you have to change view to see where they are, very annoying in the item world where the layout often tends to have higher areas.