Really? I thought it's always been that HDR was notorious on Windows, hopeless on Linux, and only really worked in a plug-and-play manner on Mac, unless your display has an incorrect profile or something/
Works well on Linux, just toggle a checkmark in the settings.
MacOS does wash out SDR content in HDR mode specifically on non-Apple monitors. An HDR video playing in windowed mode will look fine but all the UI around it has black and white levels very close to grey.
Edit: to be clear, macOS itself (Cocoa elements) is all SDR content and thus washed out.