Immortals Fenyx Rising is another from Ubisoft as they continue putting their games back on Steam, and sadly this release seems a bit messy on Steam Deck.
Thankfully, there's no annoying launcher issues here. While it does have Ubisoft Connect, much like Assassins Creed Valhalla, it worked out of the box. Although sometimes the Ubisoft Connect pop-up wouldn't go away, needing SHIFT+F2 set in Steam Input to load the overlay and disable notifications from it completely. The overlay itself also doesn't go away when you load it, so you need to then restart if it happens.
Sadly, there's a number of issues with the actual game directly. Firstly, they didn't even give it a controller configuration. So before starting, you need to go into Steam Input and set it to a gamepad as it defaults to mouse and keyboard. After that, you then get greeted by an intro cut-scene that will either have completely broken audio or go repeatedly badly out of sync. The audio issues persist in the game itself directly too. Side-note: even on desktop Linux the audio issues happen too.
Another problem is the grass rendering, it has a load of black line flickering across multiple testing graphics configurations. So right now, it's not something I'm going to suggest anyone pick up.