Hi there,
I'm Cherrelyn, an Independent Advisor here in the Microsoft Community. Thanks for your question and great setup, by the way!
Yes, Windows 11 does support HLG HDR, and with your NVIDIA RTX 4070, 4K HDR display, and 1000+ nit brightness, your system is capable of displaying HLG content correctly as long as the app you're using supports HLG decoding.
Make sure:
-HDR is turned on in Settings > System > Display > HDR
-Your media player supports HLG (e.g., VLC, MPC-HC, PotPlayer)
-NVIDIA Control Panel is set to 10-bit color, RGB or YCbCr 4:4:4, and Full Range
Let me know the app you're using, and I’ll gladly help check its compatibility!
Warm regards,
Cherrelyn