Fix: Go to garrysmod/settings/ and delete textwindow.txt. Restart the game.
A "non steam" version usually lacks the Valve assets. You need to copy the following folders from an existing Source game (if you own CSS or HL2 on Steam, use GCFScape to extract them):
If you don't own these, look for "Source Base 2007 Assets Pack" on archive forums. gmod 11 working non steam free
GMod drops to $2.49 during seasonal sales (Summer, Winter, Halloween). That’s less than a coffee. At that price, the time you spend avoiding malware is worth more than the money saved.
You might want this version to play with friends for free. Here is the reality of GMod 11 non steam multiplayer: Fix: Go to garrysmod/settings/ and delete textwindow
The Workaround: Use LAN multiplayer. If you are in the same house (or using a VPN like ZeroTier), the host types sv_lan 1 in console. Clients type connect [Host_Local_IP] (e.g., connect 192.168.1.105). It works flawlessly.
If your concern is performance (not money), the official Steam version runs on almost any PC from the last 15 years. Minimum requirements: If you don't own these, look for "Source
Disable workshop addons and lower settings — GMod will run smoothly even on a netbook.