Hi, I saw your removed my edit by stating that Vulkan on Quake remaster support Exclusive Fullscreen but this is false, and you can easily see it by the fact that g-sync (on fullscreen mode) doesn't engage at all. You can alt-tab all the time you want on Vulkan and g-sync won't engage since the game on Vulkan isn't Exclusive Fullscreen or use Flip Model.
Once you switch to DirectX 11 as I mentioned you will have actually Exclusive Fullscreen and functioning g-sync.