Works exactly as expected.

Works great on Linux not counting
Hangs on alt tab when using exclusive full screen, works fine in borderless
No performance or other major issues

An rpg with similar mechanics to the megaten family of games. If you enjoyed those games then you'll like this
Works great since day one. Not quite finished yet but tens of hours in

gamemoderun %command%
Played through the whole game without any issues.

Works perfectly out of the box
Aside from the poor optimization (the same as on Windows), the game runs flawlessly out of the box.

mangohud %command%
playing at 1440p is fine. frametimes are good and comparable to Windows. Playing in 4k is significantly slower than Windows. 4k runs at 45 fps where Windows is at a smooth 120 fps.

The game runs well enough when set to 30FPS. However, it barely ever reaches 60FPS if you set it to that
Most text in the game was fine for me to read. However, there are menu elements throughout the game that are pretty small. It is hard to read on both the deck's screen and when connected to a TV.
Metaphor runs well enough when set at 30FPS. 60FPS is not recommended as it drains the battery a lot faster
Works super well out of the box - no tweaks done

WINEDLLOVERRIDES="winmm=n,b" %command%
Frame limiter enabled at 30fps. Can be played at 40fps with MetaphorFix, however can be very power hungry.
Some UI text can be difficult to read
Near constant FPS drops, struggles to even reach 50fps. Installing MetaphorFix (https://github.com/Lyall/MetaphorFix) with LOD set to 7 and Shadow Quality set to 1024 allows the game to be played at 40fps with some drops to the mid 30s. With the in-game graphics settings set to 100% render resoution, Ambient Occlusion off, Texture Quality Normal, FPS limit set to 60fps and the deck limiter set to 40fps.
Just works

Works great
Played it vanilla, also used Lyalls' MetaphorFix for a bit. No issues with either.

Without tinkering runs at a pretty stable 30fps, with tinkering can get a mostly stable 40fps
WINEDLLOVERRIDES="winmm=n,b" %command%
Mapped the right touchpad to a zoom in case there was small text.
Locked refresh rate to 40hz and in game fps to 60. Ambient Occlusion off and Texture Quality set to Normal.
Some text can be small.
Recommend install MetaphorFix. Not for 16:10 as the UI will abruptly cut off where the extra space of a 16:10 screen begins but for Analog movement and to reduce LOD to 7 and Shadow quality to 1000. Dungeon areas and smaller areas run perfectly at 40 fps. Larger enviorments like the first town market area and the harbor town can drop to around 25 fps at times. Installing the fix above can raise fps to a more stable 30 making drops less noticeable from 40.

Works flawlessly out of the box - no tinkering needed
No issues whatsoever. Just click install and start playing this masterpiece of a game.

Manually capped the frame limit and GPU Clock in the Performance settings
I enjoyed the game (I spent 100+ hours on it), but you should probably play this on a console or a heavy duty PC if you have the option.
The game crashed on me multiple times unless I manually capped the FPS and changed the graphics settings to medium or low. The game played fine for me once I made those changes.
WINEDLLOVERRIDES="winmm=n,b" gamemoderun mangohud %command%

Seemed to just work OOB.
I had issues seeing one collectable, but a later one showed up fine. I have no idea if this was a graphical issue or I just missed it somehow. Either way, if there's graphical issues, they're so minor as to be ambigious.

Stable 60-70 FPS at 4K (100% render scale) with SMAA. Some areas (e.g. gauntlet runner) might dip to 40ish.
Save from demo did not transfer. This is due to how Proton handles prefixes. Demo save data was in another prefix, needed to copy over. Follow official guide for Steam Deck by Atlus to fix this.
Great experience, runs out of the box.

gamemoderun %command%
Significant performance degradation in fullscreen.
Controllers not detected after disconnect until game restart.
Low FPS, especially in specific areas and menus
Works perfectly out of the box

Locked to 30fps ingame, kept refresh rate at 90hz.
Text is a little small, on map screens and item shop descriptions.
Framerate still drops in the more dense town areas, like Brilehaven. But Valve have recently pushed out a hotfix that supposedly improves this.
Game issue, never experienced on Deck but cutscenes can frequently freeze for seemingly no reason.
Power draw at 8-13w and battery life at 3-5hrs.

Works great OOTB
Fullscreen is a bit finicky when alt-tabbing, but I've mostly been able to continue playing.
The patches have really improved performance since launch, stuttering and low frame rates have mostly disappeared for me.
It just works.

disabled backgrip buttons because they were just remappings of A, B, X and Y buttons. i accidentally kept pressing them....
some text was hard to read in the beginning. i got used to it though.
sometimes the game froze after resuming from sleep. this froze the whole console and i had to restart the steam deck. it got better with an update of the game but still occured occasionally. glad there were auto saves....
I played the game from start to finish on the steam deck. (I just unlocked the platinum trophy today) There was one issue where an achievement didn't trigger. The buggy achievement in question was the sword riding achievement. and apparently it's highly buggy, not only on the steam deck... had to finish the buggy achievement on my PC unfortunately...

My 20 hour save-file from the demo did not carry over the the full game.
I recommend playing with the render resolution at 125% if you play at 1080p.

40fps/40hz
Most of the text in this game is really small.
Transfering a save file from the demo to the full game needs to be done manually in desktop mode.
Game works great out of the box. A handful of shopping areas have low fps but it doesn't affect the main gameplay. Text is really small on Deck's screen.

WINEDLLOVERRIDES="d3dcompiler_47=n;dxgi,winmm=n,b" gamemoderun mangohud %command%
60-80 FPS, max settings, 150% rendering resolution (1440p). I used Lyalls' MetaphorFix mod to skip the intros and force controller buttons to be on https://github.com/Lyall/MetaphorFix I also used https://github.com/kevinlekiller/reshade-steam-proton to use reshade to inject SMAA and AMD FidelityFX CAS to get rid of the jaggies and to make the image nice and sharp (CAS makes a HUGE difference, you should try it out)

Ran fine on my Bazzite Desktop, and SteamDeck. No Controller issues at all, it auto switched between M&KB and Gamepads on the fly fine.
Just installed and ran, I am going to look into the wide screen and other tweaks later. Zero issues that I noticed.

WINEDLLOVERRIDES="winmm=n,b" %command%
Works out of the box at a locked 30fps at 1280x800 with max settings and 100% render res. You should probably install MetaphorFix by Lyall if you want fixes for analog control and full 16:10 display support, otherwise it default locks to 1280x720/16:9
If you want a solid 40fps you need to install MetaphorFix and tweak the shadow settings and LOD draw slightly alongside adjusting in-game settings.
In your MetaphorFix.ini file, change the following variables: [LOD] Distance = 7
[Shadow Quality] Resolution = 1024
In-game change: Ambient Occlusion to Off Texture Quality to Normal
After making those adjustments you can lock the game at 40fps/80hz using the Steam Deck's built in performance settings and enjoy performance that seemed only impossible a few days ago.

Everything including the movies works right out of the box.

Runs pretty great.

This is another report. I found a fix regarding the graphical issues and models not loading for Lyall's fix mod.
WINEDLLOVERRIDES="winmm=n,b" %command%
Lyall's Mod
For the fix, disable all the graphical tweaks (i.e display FOV and such) in the ini file. You can run the other mods, just disable all the graphical ones.
I need to test with gamescope and such to see if it works there as well but that's an update.

Limit to 40fps
Some texts can be small, like items description
Small issues in the 1st city. Haven't discovered others cities yet