
Alt-Tabbing in fullscreen results in an immediate crash.

Works perfectly out of the box
Played the whole game (incl. all side missions & dlcs). No issues with the launcher either.

Tried Experimental, GE, hotfix, no success. Tried swapping the .exes names too. But, sadly, was never able to open the game.
Borked

Changed Launcher.exe to BorderlandsGOTY.exe and renamed BorderlandsGOTY.exe to Launcher.exe
Overall its a great game with minimal tinkering required.

I have played this game back in 2019, but can't launch it anymore
Tried various Proton versions, including hotfix and experimental, nothing worked.

Fullscreen would often initiate at a much larger scale than the actual screen.
Slight stuttering. Fix by changing Framerate Locking to 60 FPS.
Checks cloud, steam attempts to launch and then stops the game.

renamed EXEs
Had to rename "Launcher.exe" and "BorderlandsGOTY.exe" to eachother to launch the game, otherwise the launcher says "Steam installation cannot be found" (simply adding as non-Steam game also worked)

Works great out of the box
I'm stuck at 90 fps for whatever reason, but it's fine. Played about 4 hours at once with a friend in coop, did not encounter a single disconnect or any other sort of issue

Works fine.
My monitor is 144 Hz and the game randomly changes it to 60 Hz, causing stuttering, usually after teleporting to new area but sometimes it gets wild. Though I suspect the game itself, most likely not because of Proton.

Works just like Windows, bugs and all
Had to set "framerate locking" to "unlimited" to fix the constant stuttering.
The stutter problem is also on windows, so I don't blame proton for it.

Fine for singleplayer, but loading times are unacceptable when your buddies have to wait for you on every single loading screen.
Very long loading times despite using a Samsung 980 Pro. Almost two minutes to start the game, 45 seconds for every loading screen.

%command% -NoLauncher -NoStartupMovies
Had to change Launcher.exe to Launcher.exe_old and madea copy of BorderlandsGOTY.exe to rename as launcher. Force the use of experimental, and then add commands I normally use for Borderlands 2 and presequel to start and then it worked fine.

Set WillowEngine.ini as read-only after setting graphics settings the way I wanted them to prevent a known issue with Enhanced that resets several video settings on every start.
If the in-game VSync option is enabled, combat can cause inconsistent framerate dips that do not happen if you disable it. Turn off VSync and use SteamOS's own framerate limiter.
If you run into strange framerate drops during combat or looking around in certain locations, disable the in-game VSync setting and use SteamOS's own framerate limiter.
You can still do config edits to resolve certain known issues with the Enhanced remaster as listed on PCGamingWiki, but they're less neccessary on Steam Deck since you won't be using a mouse. If you're playing co-op you'll still want to disable VOIP through the config to solve the desync issue, and setting WillowEngine.ini as read-only is recommended to stop the game from resetting several graphics settings on every start but not a requirement.

Fixing mouse input, disabling VOIP, and setting engine config as read-only to work around known issues with the remaster that are identical on Windows
Works out of the box just fine, but several known problems on the Enhanced remaster include wonky mouse smoothing with uneven vertical sensitivity, co-op desyncing because of VOIP packets and framerate caps, and some graphics settings that reset on every restart because of a poorly made launcher (even if you disable it in the in-game settings). These same issues are all present on Windows and can be resolved with editing the game's config files. These fixes can be found on PCGamingWiki, and the location of the config files are under:
~/.local/share/Steam/steamapps/compatdata/729040/pfx/drive_c/users/steamuser/Documents/My Games/Borderlands Game of the Year/WillowGame/Config
To resolve some of the graphics settings resetting on every start (such as the texture filtering setting), you'll have to set WillowEngine.ini as read only once you have everything set the way you want.

Runs excellent out of the box
Played multiplayer for 2.5 hours without issues.

mangohud %command%
Works perfectly fine. Experienced known video memory leak when playing cutsceen (via mangohud), but not really a problem with 16 GByte video ram. Friendes with whom i played together experiences the bug on windows too. Every now and then restarting the game solves the problem.

Flawless OOTB
Didn't encounter any problems. Ran at a 100% stable 165 FPS too.
Swap the names of Launcher.exe and BorderlandsGOTY.exe and run with Proton Experimental and your good to go.

Steam OLED 512GB. Ran on NVMe disk instead of SD. 1280x800 @ 60 FPS, ran flawlessly on Ultra settings.
Disable in-game once launched for the first time
Roughly 3 1/2 hours battery om max setttings, no crashing or stuttering.

Stutter fix that worked for me:
- switch to Proton 7.0.6
- run game
- close game
- delete proton files
- run game again
- set following video settings, in the main menu (IMPORTANT!)
- Fullscreen: Fullscreen
- Resolution 1280x800 60Hz
- Vsync: off
- Framerate locking: 50fps
- Anisotropic filtering: 2x
- Anti-aliasing: fxaa
- Dynamic shadows: on
- Shadow detail: medium
- Bullet Decals: On
- foliage: High
- Texture: High
- Game detail: medium
- Ambient Occlusion: On
- Bloom: Off
- Depth of field: Off
- Flare Outs: On
- Level of detail: High
- Load your game and should be smooth 50fps. If not then repeat from step 4.

Use either full KBM control scheme or full controller input scheme. Game does not respond well for mixed inputs.
Flick Stick control scheme
set gpu clock at 700mhz and TDP at 7 watts as other suggested
Not really a problem with a launcher, you can disable it in-game for future launches without issues
If you try using mixed controller/mkb inputs like gyro/flickstick you will get almost constant freezes/stutter (every 5 to 15 seconds) so avoid using that
Game is running perfect aside the problems I mentioned without touching any settings. Also, change resolution within the game options to 800p. (or within a launcher at first time boot).

Added as a non-steam game and laucned using the BorderlandsGOTY.exe. I used proton GE and it has run flawlessly with no tinkering for well over 15 hours of play now, not a single issue.
everything maxed, but not shadows
Sometimes the game would launch directly to the start screen but would be unresponsive until it plays the developer/publisher cinematics.
Everytime the game has to process vulkan shaders it will crash the first time but will launch normally if one tries again.

-windowed
Had to turn off framerate locking to fix massive stuttering.
In order to get the game to work you need to "Browse local files" and then go under Binaries/Win64 and swap the names of Launcher.exe and BorderlandsGOTY.exe. For example, rename Launcher.exe to something else, such as Launcher2.exe, then rename BorderlandsGOTY.exe to Launcher.exe, and then rename Launcher2.exe back to BorderlandsGOTY.exe.
Without tinkering, the game does not launch.
Didn't start, even after the renaiming of Launcher.exe and BorderlandsGOTY.exe ...

Launch game with default settings and disable launcher
can be hard to read gun pickups due to steam deck res

Launch Window touch-only input
Apart from the touch-only launch window, great OOTB

gamemoderun %command%
Set your maximum FPS to a specific value (30fps, 60fps). The by-default "Smooth 22-60fps" limiter causes low and unstable framerate.
Worked on Proton GE

The launcher freezes frequently. Use in-game options menu instead.
Has the same problem as the original version - there's a lag spike every 10 seconds of gameplay, regardless of settings or Proton version.
50 fps limit, 7 watt tdp, gpu clock set to 600 mhz
Touching the touchscreen by accident while playing (so not in your inventory) will send your screen spinning at mach 5 instead of moving it a reasonable amount.
Installed on the sd card with no issues, runs well even with some settings adjusted in favor of battery life.
Played the co-op campaign from start to finish with a friend over the internet who was playing the game on Windows 10, everything worked fine and no issues were encountered.
Played the game with ultra graphics settings and VSync enabled.

The game reported that I was offline, thus I was unable to even really play the game, as co-op was what I had intended to do, here.
In addition to the online issue, it's probably worth a note that the game yelled at me about how my PC's specs are below the minimum requirements, even though I'm pretty certain mine exceed even the recommended requirements, so that makes me wonder if the internet issue was because it just couldn't detect any of my hardware or other setup at all. That's just a guess, though. Good chance I could be wrong.
Rename BorderlandsGOTY.exe to Launcher.exe and Launcher.exe to BorderlandsGOTY.exe