Setting gfx_vsync to 0 causes G-Sync to be engaged unintentionally.

If G-Sync is enabled & gfx_vsync is disabled or set to 0 then V-Sync should be actually disabled.
G-Sync is engaged unintentionally when the desired behavior is for V-Sync to be off at the game level.

According to this documentation post: https://learn.microsoft.com/en-us/windows/win32/direct3ddxgi/variable-refresh-rate-displays#variable-refresh-rate-displaysvsync-off
It specifies for V-Sync off or to support variable refresh rate displays (G-Sync), the application must opt in for screen tearing.

The game doesn’t do that, resulting in the mentioned issue. This can be verified using a tool called PresentMon: https://github.com/GameTechDev/PresentMon

Incorrect Behavior: Game calls IDXGISwapChain::Present(0, 0) resulting in the mentioned incorrect behavior.
Correct Behaivor: Game calls IDXGISwapChain::Present(0, DXGI_PRESENT_ALLOW_TEARING) results in the correct behavior.