After finding out the Use Display Luminance setting is only effective when the Dolby VSVDB is V1 (and I think most would have V2 Displays), I am now thinking - is it actually relevant/helpful?
Unfortunately the values it is changing go into proprietary code so cannot tell ultimately what it is doing from the code side.
During your testing, did you see any difference with this setting on or off?
I am thinking to take away the UI setting, and just have it set to always on in code to avoid user confusion, it has some small real-world value from the logging perspective to check the VSVDB has actually changed for my V1 TV, and I recall in graphics mode it did have some effect - but we always want video mode.