By default the engine uses Direct3D on Windows, Metal on macOS, and Vulkan on Linux. If you are experiencing issues related to one of these graphics APIs you can try OpenGL as a fallback with this launch option:
- Right-click Unturned in your Steam Library
- Select Properties... to open the General tab
- Find the Launch Options field
- Type "-force-glcore" without quotes
Note that performance with OpenGL will be worse, but in general older devices have better compatibility with OpenGL than the newer graphics APIs.