Sony FX 6 Quick Start Manual page 107

Cine EI: Turning on a LUT for the viewfinder (VF)
VERY IMPORTANT!
It helps to use the waveform monitor in the VF to judge Slog 3
exposure. The waveform in the VF measures the output from the SDI
and HDMI outputs, even if there is no recorder or monitor attached.
So, to avoid confusion, even if you are not using an external recorder,
turn on the LUT for the SDI and HDMI outputs if you are turning on a
LUT for the viewfinder.
This will ensure that signal measured in the waveform monitor
corresponds to what you are seeing in the viewfinder: the normalized
image from the s709 LUT.