DIAGNOSIS You're describing the "soap opera effect" caused by Auto Motion Plus (Judder Reduction), which is likely set to Auto or Custom with high values.
FIX Turn it OFF completely for film content. While playing your movie or show, press the Settings button on the remote. Go to Picture > Expert Settings. Find Auto Motion Plus. Set it to Off. This is the only setting that completely disables frame interpolation.
IF THAT DIDN'T WORK Ensure you're not in a dynamic picture mode like Vivid or Dynamic. Switch to Movie or Filmmaker Mode, which have these settings disabled by default and provide the most accurate motion.
HEADS UP Settings are often per input and per app. You'll need to disable Auto Motion Plus for each HDMI port and for the internal apps (like Netflix) separately. Use the same steps while content on that source is playing.