Game runs flawlessly out of the box. Tinker steps are not really needed but can help to further optimize performance.
gamemoderun %command%

Works great after the first cutscene
Durning the first cutsecne multiple voice lines were over lapping with each other.
Some of the begining cut sences were broken and would not play but you can get past them by skipping them.

The game asked me to install some Microsoft dependencies. I clicked "Accept". They installed and the game launched without issue.
I received this game on Epic Games and added it to Steam via the Heroic Launcher. I set the settings to Medium and played happily in Edgewater (the first town) at 55-60 FPS. Happy with that.
I'm not far through the game, but happy so far!

The prerecorded cutscene in the Murder on Eridanos did not play correctly until I have switched to Proton GE.
I have finished the base game and the DLC on the Deck. They all worked flawlessly aside from one cinematic.

No issues with playing the game, plug and play experience
My PS5 dualshock wasn't immediately recognised, and the button symbols were default set to the Xbox style.
Controller input is set to xbox button style. but using steam controller "Enable Steam Input" settings worked fine.
Woorks ootb.

Just install and play

you can actually adjust the text size but for some reason only for the menu so all the weapon stats and charakter sheet and stuff is realy hard do read would be great if the devs would change that
sometimes when you put the deck to sleep mid game and wake it up there is some crackling but it goes away after a reboot of the game
Runs realy great on the steam deck would love to see the devs adjusting the text size problem for the whole game
Game runs great, no issues

runs like native
i expierenced higher frame rates on linux than i did on Windows.

Works great, just install and play
I did have two crashes to desktop during my 36 hours of playtime, but it was no big deal because the game auto-saves a lot. Lost basically no progress at all.

Flawless (Linux Mint, default Steam proton v (8.0-3 or Experimental)
Xbox Series controller works flawlessly as well

The game runs perfectly. With Proton Experimental, it doesent show some cutscenes at the beggining. But with Proton GE its perfect.

The game ran flawlessly, however my poor laptop was screaming just to keep it self cool trying to play it. All setting low, graphics set to 720p was able to get it playable... but it was a blurry mess. You'll need some GPU power to play. I'd say a Steam Deck could probably handle it.

Mostly performs as I would expect but crashes are quite frequent but don't occur consistently
gamemoderun %command%
Very freuqent crash to desktop
Got stuck in dialogue once
Framerate locked to 30; Thermal Power (TDP) Limit set to 12.
Just install and run. No tweaking necessary unless you want to extend battery life. Runs great on high settings.
Just install and play. Works perfectly.
Crashed once or twice within 18 hours of playtime.
The Outer Worlds runs perfectly fine
I played The Outer Worlds for over 40 hours on Linux and experienced zero issues. No tinkering, everything worked out of the box. I can recommend this game for Linux gamers.

Make sure to pre-cache shaders!
Works Perfectly Out of the Box
MANGOHUD=1 gamemoderun %command%
Works pretty much OOTB and haven't experienced any noticeable performance issues.
DXVK_ASYNC=1 mangohud %command%
I noticed very occasional stuttering with DXVK_ASYNC=1 added as a lunch option but nothing that was so often or bad that it took me out of gameplay. DXVK_ASYNC=1 fixed previous stuttering that made the game unplayable for me.
For me, adding DXVK_ASYNC=1 is the most important launch option, this fixes stuttering that made the game mostly unplayable. With that option set the game runs extremely well and on-par, and sometimes better than in Windows. Recommend giving Linux a try.

-dx11
Very impressed.

I'd get slowdowns any time something significant happened, though I am playing on max settings.
Proton-GE seems to be the only way to get ingame cinematics to work. After version 29, this is broken for some reason.
gamemoderun %command%
Only supports Ultrawide in borderless windowed, on fullscreen it's locked to black bars 1440p. However, I didn't notice any issues with playing on borderless.
Haven't tried on anything other than latest GE 35.

DXVK_ASYNC=1
Heavy stuttering with drop of framerate after a while, also when freshly loaded, like mentioned in other reports, are fixed through DXVK_ASYNC=1 launch option. Also activate shader pre-caching through steam settings.
Refresh rate and FPS cap at 40
Text is slightly small but can be enlarged in the options menu
Occasional lockup with restart required. Deleting proton files seems to prevent this recurring regularly.
Plays great. I did encounter some graphical artifacts during dialogs or companion attacks. Aside from that the gameplay experience was great
Midway into the game I encountered a graphics glitch where during dialog close ups or the companion special attacks portions of the screen would just go black. Such as on a characters faces and body, or while the companion is attacking. It didn't affect the rest of the gameplay, just on these specific points.
- Used SteamOS framerate limit option to lock the framerate to 30fps
- Set the game to medium settings
Loaded a mid game save and completed quests in Byzantium with only minor stuttering after loading a new area. Overall a great experience with PS4 comparable settings on a handheld device!
FPS drops upwards of 30FPS whenever the game loaded in assets. No matter the resolution or texture settings.
Note: This MAY just be becuase I am running off a HDD. Results may vary.
The extreme and prolonged slow-down every couple of minutes makes the game unplayable. Switching to experimental Proton doesn't fix it.
The game ocasionally has extreme slow-downs. The framerate will drop to about 5 fps and remain there for 30-60 seconds. This happened to me at least 6 times during the first hour of gameplay. When this happens, the Steam Deck's fan goes whisper-quiet (practically off), while the GPU and CPU usage remains normal. (eg. about 70% CPU usage).
Due to missing game options (like to disable blur and depth of field, no sharpening options) and the unavailability of MSAA, the game looks very blurry on a Steam Deck screen.
lowered the resolution, set to windowed, and enabled FSR. Ran at 40hz and 40 fps
No issues running on deck, honestly it's fairly impressive to have it look as good as it does on it