I'm on a MacBook Pro (16-inch, 2019) and I also see this checkbox. I didn't even think this model supports HDR.
Edit: Apparently, HDR is only supported on an external display. And if you connect an external display, it uses ATI* graphics. And you're probably going to want to connect the power adapter at that point. Which means that "Optimize video streaming while on battery" is pretty much a useless option on this model, unless it actually does other undocumented stuff.
* AMD ATI forever