I have installed Windows 11 on a machine and am running MC 28.0.66 on it. A bit of quirky behavior is present, regarding the way High Dynamic Range and Standard Dynamic Range content is displayed. In brief: With MC set to Red October HQ, HDR looks correct and SDR looks unwatchably ridiculous. With MC set to Red October Standard, SDR looks correct and HDR looks washed out.
My workaround is to switch between Red October Standard and Red October HQ depending on the content I will watch. But this kind of problem (which is likely caused by the way Win11 handles HDR) deserves a solution, if possible. Windows 11 is not officially released, so no one could expect this to get any sort of priority, but it is likely an issue coming soon...