Left 4 Dead 2 - screen flickers in gameplay

Left 4 Dead 2 on Parallels running windows 11 used to crash every time I launched it but someone on reddit pointed out I have to set the shader effects to medium or low. Now I can get it out of the menu and into the actual game, but the foreground keeps flickering out of the picture. It seems to just get overwhelmed and just flicker the sky and maybe some background buildings into the image before drawing all the layers properly. The framerate seems smooth and it doesn't matter if I set it to a lower resolution. I've tried putting it into gaming mode from productivity mode and it didnt help either. What am I doing wrong?

 

I decided to try one last thing and set the display mode from fullscreen to windowed (no border) and sure enough the flickering went away. I'm not sure if it will last but so far so good so thats what I did for anyone looking this up. Any idea why this mattered?

 

Try this as a boot flag:
video.untrimmed_dynamic_cbuffers=1
According to others, this should completely fix these flickers in fullscreen mode.

 

Graphics Settings:

• Set shader effects to Medium or Low.
• Disable V-Sync.

Parallels Configuration:

• Increase VRAM allocation in Parallels settings.
• Switch between DirectX and OpenGL for the Graphics API.

Windows Graphics Settings:

• Set Left 4 Dead 2 to High performance in Windows Graphics settings.

Update:

• Ensure Parallels and Parallels Tools are up to date.

Background Apps:

• Close unnecessary applications to free up resources.

Game File Verification:

• Verify game files via Steam.

Compatibility Settings:

• Run the game in compatibility mode for older Windows versions.