If you haven't already, download and install HandBrake from the official website.
In the "Presets" panel, select the "SDR" preset. This preset will apply the necessary settings for SDR conversion. convert hdr to sdr handbrake
In the "Color" panel, make sure that the "Color Range" is set to "Limited" (for TV) or "Full" (for PC). You can also adjust the color space to "Rec. 709" (SDR) or leave it as is. If you haven't already, download and install HandBrake