I have figured out how to get Arma 3 to work with Proton and have full mod support. After downloading Arma 3 using Steam play Proton, go to your Arma 3 directory, and rename the “arma3launcher.exe” to anything. Then rename your “arma3_x64.exe” or “arma3.exe” to “arma3launcher.exe”. After that you can just launch the game through Steam, but if you have audio issues you need to use “WINEPREFIX=/path/to/steam/steamapps/compatdata/107410/pfx winecfg”. Go to libraries, add “xaudio2_6” and “xaudio2_7” setting both to “native,builtin”. Finally if you want to use any mods that use .dlls you need to source a imagehlp.dll from a windows installation, and drop it in your “/path/to/steam/steamapps/compaydata/107410/pfx/drive_c/windows/system32” directory. Then use winecfg and set "imagehlp" to "native". That will let arma load mods that use .dlls properly.
Suggested tools for a better experience Proton Wine Manager Arma3-Proton-Launcher
