Windows always requests MSAA when creating an OpenGL context.

You can see the problem here: https://github.com/racket/gui/blob/172b7d5a561b74375004decbb68a7ab471e2c53f/gui-lib/mred/private/wx/win32/gl-context.rkt#L300

If wglChoosePixelFormatARB is present on the system (which it will be for virtually everything), it will always be called with the WGL_SAMPLE_BUFFERS_ARB attribute set, even if the number of samples is set to zero. My machine happily accepts this, despite the number of MSAA samples requested being 0, and creates an MSAA target, greatly degrading rendering performance. My GPU is a nvidia 1060, driver version 460.89. This can be easily verified with Renderdoc, where the final framebuffer will be a Texture 2D MS.

I believe the correct behavior is simply omitting the WGL_SAMPLE_BUFFERS_ARB and WGL_SAMPLES_ARB parameters when the number of samples on the provided gl-config object is 0.

Start in gui-lib/mred/private/wx/win32/gl-context.rkt around line 300, where the Windows OpenGL pixel format is selected. Inspect the wglChoosePixelFormatARB attributes and use RenderDoc or an equivalent context check to compare zero-sample and multisample configurations. Done means a zero-sample gl-config no longer produces a multisampled framebuffer, while nonzero sample requests still work.