

For multiplayer add "game_client.debug.override_processor_architecture": "AMD64", to SteamLibrary/steamapps/compatdata/1575940/pfx/drive_c/users/steamuser/AppData/Local/sins2/settings/settings.json Otherwise the CPU architecture will be wrong. Singleplayer works without this tweak.
In some cases the app would take too long to launch and the system would prompt to wait
I was able to start and play the game seamlessly without having to make changes to startup commands or the proton version.

Game starts up to a dark grey screen. Only way to escape this is to hold down the power button.
/nolauncher
Game starts, but nothing is visible. All forms of input are inoperable, and the only escape is to power down the computer. Completely Unplayable.

/nolauncher
Problem with launcher window. Just use /nolauncher
Ran the shell script to change the executable along with the previous fix of changing the config to 'AMD64', worked flawlessly in multiplayer with users on windows.

Singleplayer works perfect out of the box - Multiplayer does work with a few minor tweaks
Checked if "Staging -> Hide Wine version from applications" is enabled (it seems to be enabled by default now for Proton GE)
Multiplayer de-synces without installing a specific verison of MS vc_redis. See https://steamcommunity.com/app/1575940/discussions/5/7026264603287379799/#c7026264603289091243 for details.

No Problems

Add "game_client.debug.override_processor_architecture": "AMD64",
to SteamLibrary/steamapps/compatdata/1575940/pfx/drive_c/users/steamuser/AppData/Local/sins2/settings/settings.json
Crackling during the intro scenes of the game, but it goes away.
The only thing I had to do to get past the multiplayer join problem was add a single line to the settings.json file. This overrides the CPU architecture so it doesn't have "wine" appended to it, thus allowing you to play with others on the same AMD64 architecture. Everything else was standard Proton and standard settings.
If you have never played the game and are trying to find the settings.json file, it won't be there. You have to launch one time first, then it will be created.

Multiplayer had problems with joining, but those were fixed after following these steps (thank you, LinLo!): https://steamcommunity.com/app/1575940/discussions/1/7026264603287932608/#c7026264603290039319

Yes unless you want to play with friends.
Multiplayer doesn't work between Windows and Linux users despite identical game versions
Windows and Linux clients cannot connect to eachother

/nolauncher
Game launcher was running but not showing up properly therefore I couldn't start the game.
Add "/nolauncher" into the steam parameters if you've launcher issues and can not start the game.

started in proton with no issue, Started right up from day one of release. Played on Manjaor linux

Works perfectly out of the box.
Works perfectly at max graphical settings, at 4k resolution. No tinkering of any kind. I played for 5 hours. Currently it is using proton 9.0.2, and I did not set this manually. Also the launcher works fine, although when I click on any web link it opens the browser with an empty page. Great game, by the way :)

gamemoderun %command% /nolauncher
[For Multiplayer to work] Added this to the sins2 settings file:
"game_client.debug.override_processor_architecture": "AMD64"
Additionally some desync issues might occur in multiplayer. To fix them I executed a script. I basically followed these steps and it worked perfectly:
https://steamcommunity.com/app/1575940/discussions/1/7026264603287932608/#c7026264603290039319
Game runs perfectly out of the box (at least for singleplayer)

No issues, runs out of the box.

%command% /nolauncher
In the endgame when zooming in big battles there will be stutters that are can be really heavy. (IE: hosting a game of 8 players with one of them being a human player besides myself, the rest are medium AI). Otherwise game performance is acceptable.
Mandatory to use the following patch to crossplay with Window Users: https://steamcommunity.com/sharedfiles/filedetails/?id=3311876099
Everything works out of box. No tweak needed. No issue with launcher display. Haven't try multiplayer, so no comment on that.

/nolauncher
Significant slowdown initally, fixed by turning off fractional scaling in display settings
Stardock launcher does not load properly, use /nolauncher to avoid

%command% /nolauncher
Game does not work if I have tile windows enabled in PoPOS
After starting game steam says it not responding, but after 5 to 10 secs everything loads and works! Just need to disable tile windows if you are using popOS.

It just worked, no changes needed anywhere other than using GE, which I have set in Steams settings for 'other titles'.
Didn't try Multiplayer, as I don't play multiplayer myself.

Multiplayer is a very important component, especially when there is no campaign.
Multiplayer does not work reliably.
Apparently, the multiplayer issue has the usual fix for vc++ redistributable version. Really, this is too cumbersome even to test that the fix works, especially in a game like this, where a scenario is so long.

/nolauncher
To fix multiplayer with Windows users
- Run
protontricks 1575940 winecfg
- Staging -> Enable "Hide Wine version from applications" (requires GE-Proton)

Game lauches and runs without issue using GE-Proton9-11 Multiplayer only works with additional tinkering
- Multiplayer worked after running the following:
protontricks 1575940 winecfg
One instance of desync but "Skipping all" on both systems allowed game to continue without issue

/nolauncher
tried hiding wine version to play multiplayer it does allow connecting when doing this however immediatly desyncs after launching the game
Multiplayer doesn't work due to framework/version mismatch
you can use proton experimental don't need any special version. the problem is getting multiplayer to work which so far no version has done well without extensive work arounds. theres a few guides however as a person who has used linux for over 5 years and considers myself comfortable with linux, the guides don't make much sense and make a lot of assumptions of prevoius knowledge or knowing how to do things so i haven't gotten multiplayer to work where others have. like open proton ge with terminal what does that even mean? how do i open proton ge in terminal? or the scripts that are written to fix the problem how am i supposed to use them? no matter how knowledgable a user there will still be gaps in a persons knowledge and i can't find anyone explaining this so until a better guide is made just know single player works well. Just don't look forward to playing with your friends who use windows and if you do figure it out if you would write a guide that can be easily understood for desktop linux users especially the gratitude would truly be unending.

I am using flatpak version of Steam

Single player works, but linux players will not be able to play with windows clients out of the box.
Multiplayer not functional with windows clients
Multiplayer not functional with windows clients.

%command% /nolauncher
No Multiplayer
The work arounds listed sadly don't work for me as they need protontricks, and proton tricks won't recognize my steam installation

Only minor startup annoyance, otherwise runs flawless
Worked in every scenario I tried, only issue I ran into is at launch (with or without launcher) is it claims "app not responding" I just ignored it and waited like 10-15 seconds after that message and the game started and the message went away. No issues after in game.

Launcher invisible. Game unplayable. Just like Galactic Civilizations.
Don't buy it for linux.

gamemoderun mangohud %command%
From installation to gameplay, the entire process was seamless. The game runs smoothly, with no crashes, glitches, or performance drops. Whether you’re engaged in massive space battles or managing your empire, the game delivers an excellent experience on Linux.

лок кадров на 45
не подреживает маштаб интерфейса
Для комфорта лучше добавить внешний экран и мышь с клавой

Launched with Proton experimental.
Game launcher was somewhat greyed out, but all the functions and buttons worked and the game started. Managed to play a 2,5 hours long single player session right away and with no crashes, graphical or sounds issues to report. Haven't tried multiplayer yet. The game looks beautiful and it runs flawlessly so far.

After applying a couple straightforward fixes, everything in the game (singleplayer and multiplayer) runs flawlessly.
%command% /nolauncher
To join a multiplayer lobby with Windows players (currently only available in Wine Staging or Proton GE)
protontricks 157940 winecfg
- "Staging" Tab -> Check "Hide Wine version from applications"
Very minor crackling in the into video. Goes away completely after you make it to the menu and is not noticeable anywhere else in the game.
If you are using pipewire the crackling can be avoided completely by forcing the ALSA audio backend for the game:
protontricks 1575940 sound=alsa
Multiplayer games will desync after a few minutes. Updating the games VC redistributables fixes the desyncing completely.
See this thread on the steam discussions for a script to do this for you and more details about the process.
Singleplayer works out of the box on Proton 9.0 or newer. Multiplayer requires Proton GE and some fixes applied to the game to run but once patched multiplayer works perfectly.

Played for 5 hours now and have had no issues
No issue with saving or running the game. ran it multple times and for 5 hours now.

/nolauncher
The game works without a problem, however, Stardock's launcher is bundled, so I suggest bypassing it with the /nolauncher option.