Sony FX 6 Quick Start Manual page 144

S & Q shooting
S & Q shooting is for shooting slow motion or fast motion and time
lapse: something other than a standard frame rate.
S and Q slow motion shooting works by capturing the video at a
different frame rate than the frame rate at which the video clip will be
played back.
Shooting at high frame rates is the only way to create smooth slow
motion. Video editing software has effects that allow you to slow down
the speed of a clip. These effects rarely look good because the software
has to invent extra frames (interpolation).