Great. It has native support, only the menus and inventory are a little wonky, since you have to navigate the cursor with the sticks but I just mapped the right touchpad as mouse and problem solved.
Wow I've been playing through Grim Dawn for the past couple of days on my Deck dealing with the wonky UI controls, and I having right track pad just be the mouse would solve 99% of my issues. I can't believe I didn't just rebind it. I even went through a couple of community profiles lol