By default highlights are mapped to something comparable in brightness to 100 IRE in Rec709
A lot of people are working that way, but in my opinion it is a terrible idea.
HDR is full of unknown possibilities, but making it look like 709/ gamma and trimming up some highlights does not make good HDR in my opinion. It os a safe compromise to shoot for SDR and get an HDR master but it does not exploit the potential benefits of HDR - images that are more real, bright colors under or from bright lights, increased contrast and therefore sharpness, emotional DR shifts etc etc.
Certainly SDR images can be mastered in an HDR wrapper, just like black and white images can be mastered in a color wrapper and yes there will be times when that is appropriate. But why not use HDR for what it is - there are so many good creative possibilities why deny them.
Just my opinion as a colorist
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