It appears HDR is broken in-game.
When attempting to adjust the HDR in-game, it gets darker no matter which way you slide until you go back to 100%, and it seems to brighten a bit, but the game is still too dark. The general brightness slider just makes the game appear gray and washed out.
I’m still exploring settings on my graphics card, in Windows, and in-game but am a bit stumped at the moment. If I come across a fix, othere than turning off the HDR in-game, I’ll drop it here.