Came here to say this. It just cranks the brightness up for the pixels. But if you are already at 100% there is not much headroom so all the "before and after" for me were pretty hard to differentiate. There was some minor difference if I studied it closely but I'd probably not notice it during normal use it was so slight.

If I went down to say 50% brightness then it was much more pronounced, but who lives their life with their eyes only half open like that?!

That's what I'm finding as I researched it:

Android's HDR brightness slider is low - The single most common "HDR does nothing" report on Android 15/16 devices. Samsung also has Super HDR/Extra brightness / Vision booster toggles under Display. Any of them at the conservative setting would have an effect.

I’m known for having my brightness down to the minimum at all times. The demo page effect is very pronounced. Effectively, it is ignoring my system level preference which makes me hate it a lot.