1. Make sure you're on the x86-64 Branch

2. Download and Use https://github.com/solsticegamestudios/GModCEFCodecFix

3. Run CEFCodecFix. Make sure you're launching GMod through CEFCodecFix at all times, otherwise Steam might overwrite the patched files. Make sure it's run through your terminal.

Notice: If you're still experiencing crashes then it's likely you've didn't run it through CEFCodecFix at all times. Also check this out: https://wiki.archlinux.org/title/Steam/Game-specific_troubleshooting#Game_does_not_start_6

Notice 2: Arch Steam Native Runtime doesn't work with Garry's Mod and will crash it.

Notice 3: Please don't attack the project as a way to get back at me for anything. It'll just make everybody's day worse as I have zero connection to the project itself.

1. Make sure you're on the x86-64 Branch and Force the use of a specific Steam Play compatibility

2. Go to https://github.com/robotboy655/gmod-lua-menu OR go to https://github.com/solsticegamestudios/GModCEFCodecFix

3. Download the zip file and open it or use the codec to fix it

4. Extract contents of gmod-lua-menu-master folder ( folders lua and materials ) to your SteamApps/common/GarrysMod/garrysmod/ folder. This step isn't needed if you're using the codec fix itself.

Your menu is likely not showing.

1. Make sure you're on the x86-64 Branch

2. Download and Use https://github.com/solsticegamestudios/GModCEFCodecFix

3. Run CEFCodecFix. Do not start yet.

4. Go to https://github.com/robotboy655/gmod-lua-menu

5. Download the zip file and open it

6. Extract contents of gmod-lua-menu-master folder ( folders lua and materials ) to your SteamApps/common/GarrysMod/garrysmod/ folder. You should be able to play without issues now.

Pros for Linux build: You will not experience any crashes or any bugs related to sprays in my experience as long you follow what I've said.
Cons: You will not get the Steam overlay because Facepunch hasn't patched it to work. Also only uses OpenGL instead of Vulkan which is the cause of a lot of bugs not stated here. Text might look strange due to the fact you don't have the MS fonts downloaded.

Pros For The Proton Version: Should run perfectly fine regardless of anything stated here. Steam overlay also works with this method.

Cons: Low FPS and crashes have been experienced by me with this method. Plus you won't be able to see sprays ingame if that is something important to you.