The screen flashes when VSync is toggled on or off. This only happens with Vulkan with Exclusive Fullscreen on and it does not happen using OpenGL with Exclusive Fullscreen on nor does it happen using Vulkan with Exclusive Fullscreen off. This is a bug that has existed since the first 26.2 snapshot.
Steps to reproduce:
1. Launch the game with Vulkan and Exclusive Fullscreen on
2. Toggle on/off VSync
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Update: As of 26.3 Snapshot 4, toggling VSync with Exclusive Fullscreen disabled (Borderless) is also affected.
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Update: As of 26.3 Pre Release 2, Borderless Fullscreen is no longer affected.
Environment
CPU: Intel Pentium Silver N5000 GPU: Intel UHD Graphics 605
Update: I have managed to grab a screenshot of the white flash I was talking about. It appears that whatever shows up in the window before hitting F11 to fullscreen can show other stuff upon toggling on/off vsync. My drivers are up to date and have been up to date for some time now. (31.0.101.2141)