Since it seems there are no easy guides available on this, I figured I would make one for everyone. This guide was made on Kubuntu 18.04, however, it should apply to most platforms.
Step 1. Open Steam
Step 2. Go to the Library tab which has all of your games
Step 3. Right-click Garrys Mod, and choose properties
Step 4. This will open up your in-game settings like so. Navigate to the tab called BETAS
Step 5. Choose the beta which starts with x86-64. The wording will differ depending on your platform, but it must start with x86-64.
While you are indeed by the definition of steam installing a beta, this is by far the most reliable branch of Garrys Mod. You will encounter some weird things at times, but mostly if you are a sorry fool like me using Linux :)
Alright, everyone, that concludes how to get 64-Bit Garry's Mod installed! If you found this guide helpful, make sure to check out our servers!
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