When enabling HDR mode in 32-bit Preview the image is typically too dark. Now, this is probably due to the fact that my monitor, although supporting HDR and WCG, only covers HDR 400 instead of, say, 1000. However it is not uncommon that displays ( if not targeted specifically at content creators ) have lower peak luminance than HDR10 recommends. That makes it necessary to increase exposure by two stops to get roughly the same brightness as the corresponding SDR-rendered image. It would be more comfortable if the 32-bit preview either saved the exposure setting ( as it does with the reference white setting ) or, even better, if there were an option to input the peak luminance of the used display and have AP and AD adapt the brightness levels automatically.
By the way, the exposure setting does not influence the brightness of transparent backgrounds, so they will remain gray instead of white. It might be worth thinking about modifying this behavior.