First, I know there is an in-game set up guide. But it's just one of those "adjust your brightness until x/y/z logos are not visible/barely visible/clearly visible" things, and those generic set up guides are rarely ever optimal.

Second, don't be the guy who says "if your TV is set up properly, you shouldn't need to change the game's brightness settings", because that's just not true. The default settings can't account for hundreds of different displays and their respective calibrations.

"UI Level" is obvious what it does.

"Max Display Brightness" is the one that Im having an issue with. I assume it translates to max luminance. The problem is, they just have a 0-100 slider instead of a slider with actual nits/candela values. The max luminance for my display for example is roughly 850 nits/candela. I have no clue how their slider translates. 0 obviously isn't 0 nits, and 100 could be anywhere from 1,000 to 10,000 nits.

"HDR Brightness" seems to control the contrast or maybe the overall brightness.