Steam Deck --

[Kn0whereMan]

I got the game to install and run perfectly on the Steam Deck. The only caveat being you will have to tinker with the controller mapping because the default is less than perfect. There are some duplicate mappings and some functions left out and some functions mapped to buttons that are either difficult to use or don't feel right. Other than the controller layout and mapping the game performed reasonably well on the Deck.
It does experience slowdowns just like on the desktop. I haven't done any battery testing yet to see how much juice the game pulls so I couldn't tell you what kind of battery life you'd get playing Shadows of Doubt on a full charge. At a glance it didn't seem to pull too much juice. It may depend on how large your city is and how much time it spends crunching a new city and all that.
The background simulation didn't seem to pose an issue for the Deck. It moved right along with all the denizens of the city going about their business without choking on anything. With the controller mapping and control scheme properly set it plays brilliantly. You will probably want to turn off some graphical features. On the Dec's screen you really don't need temporal anti-aliasing. Things like that that will free up processing cycles for the game and possibly save you some battery life. The bottom line is that it's perfectly playable with a little tweaking and, just like the desktop, would benefit from some optimization, which I'm sure will happen at some point...

[jbfink]

Do you mind sharing particulars of your setup on the Deck? e.g., did you use GE-Proton or Experimental or anything, did you mess with any of the Deck settings re: TDP etc, the resolution you set it to or other graphical settings? I haven't bought the game yet, but it's really been on my radar for a good long while now and I've been a little bit reticent to pull the trigger because most reports of it on the Steam Deck mention that it's fairly slow.

[Kn0whereMan]

I used the standard default latest Proton version. Nothing exotic, no extra settings. Straight vanilla Proton. The slowdown issues aren't game breaking. It's similar to the slowdown the desktop experiences. I have my Deck set with a 40hz/fps limit. The slowdown on the Deck is a little more pronounced than the desktop because of the hardware but it is still perfectly playable. Didn't bother me all that much. The devs are aware that the game needs some optimization so it will get better over time. There may be moments where the slowdown gets worse and I just haven't experienced them yet, I don't know, but in my playing time it hasn't been too much an issue. I just recommend limiting all the extra graphical bells and whistles that you probably can't see on a 7 inch screen anyway. I suppose I could test it out using Glorious Eggroll and the like to see if there's a difference in performance.

- If you already know about ProtonUp-Qt and Glorious Eggroll, disregard this next bit...

If you don't already know, and this is for all Steam Deck folks, there is a utility you can install and run in desktop mode called ProtonUp-Qt. When you fire up the Discovery package manager you can search for it. ProtonUp-Qt will install various exotic flavors of Proton, like Glorious Eggroll. It does everything automatically, putting the packages where they need to go and the like, and will even let you see which games you have that run this version or that.
Glorious Eggroll is a flavor of Proton, Valve's compatibility layer for running Windows games (based on WINE), that has had significant tweaks and hacks and additions made to it to allow it to run certain games that vanilla Proton doesn't run or doesn't run well. For manual installation (for the experienced only) you can download the latest release here http://github.com/GloriousEggroll/proton-ge-custom/releases