This is not my own work by any means, but I really wanted to get this game to work and 'areweanticheatyet' didn't show the solution, so though you may want to add it in the comments for that game. PS steamdeck=1 as the launch command DID NOT work for me.

Personally, I tried the simplest method: changing the one game's compatibility option to a lower proton version (8.0-5), which worked the first time for me. However, here are other options should that not work:

tomayy [has Dark and Darker] 6 Sep @ 5:23pm
2
Hey all I figured out how to finally play and get past the tavern.exe issue. Tried a ton of combinations of launch options and proton versions. Turns out none of the launch options helped at all and we don't need steamdeck=1 anymore if you're on linux.

Use Proton GE 9-7 and it will work without any required launch options. Any proton version 9-8 and later will break.

For the windows users I don't have a solution but you can try some of the launch options I found below to see if you can make it work:

-server=http://54.148.133.180:30000 -steam=1 -taverntype=steam -tavernapp=dad

SOURCE:
https://steamcommunity.com/app/2016590/discussions/0/6057990917763531224/

lynchy901

All known methods to run Dark and Darker on Linux

PSA: I noticed it was hard to find all of the known methods to run Dark and Darker on Linux. I have created a github repo here that I plan to keep up-to-date with all known methods: https://github.com/nmlynch94/Dark-and-Darker-Linux/blob/main/README.md. Contributions welcome if any others are known.

SOURCE:
https://www.reddit.com/r/DarkAndDarker/comments/18uayiv/all_known_methods_to_run_dark_and_darker_on_linux/

Dark and Darker via flatpak

https://github.com/nmlynch94/com.darkanddarker.DaD/blob/main/README.md

Hope this speeds up fixing this game for someone out there :)