This guide will show you how to fix Garry's Mod not launching on macOS Catalina (10.15)
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Step 1: Download Garry's Mod normally and add all the necessary content (CSS, Half-Life, etc.)
Step 2: After you have installed Garry's Mod, right click on it in the Steam library and select properties
Step 3: In the properties tab, click on BETAS and select "x86-64 - Chromium + 64-bit binaries"
Step 4: Let Garry's Mod update and, once done, verify its integrity
Step 5: Launch the game and enjoy!
Thank you for reading this guide & I hope I helped you out.
