Since version 3.13, there is no need to manipulate anything to have an automatic conversion HDR to SDR. New conversion works on the luminance curve and the chrominance. A 3D LUT is dynamically applied to convert BT.2020 to BT.709.
To have an optimal conversion, here are the settings that we advise :
Deep Color: 10 Bits
Color Space: Y'CbCr 4:4:4