Yep, very used to seeing that for real-time rendering that is composited by DWM. However…
Since the above, I’ve learned more about this, and there is (at least on NVIDIA drivers) a fairly straightforward way to get fast path rendering to the display rendering purely with OpenGL on Windows 10. In PresentMon, it’s called “Hardware: Legacy Flip”. In this mode, the rendered swap chain image bypasses WDM composition and most of WDM’s overhead, permitting VSync to the display rather than WDM’s virtualized VSync.
On a single GPU system (NVIDIA GPU), you obtain this the same way as usual for Full-screen Exclusive windows (fullscreen window with focus, etc.). On a multi-GPU system, you’ll need a vendor-specific “trick” to bypass DWM composition and force flip presentation mode. This is all with a pure GL app.
Of course via Vulkan, there’s now direct mode which lets you take whole monitors away from DWM and render to them directly. That’s an alternative: Render with GL and display with Vulkan.