DIAGNOSIS You're fighting the default "Auto" Motion Plus settings. They're overly aggressive out of the box, creating the "soap opera effect." The settings can also behave differently per input and app, which is frustrating.
FIX Press the home button, go to Settings > All Settings > Picture > Expert Settings. Find "Picture Clarity Settings." Here, set "Judder Reduction" and "Blur Reduction" to 0. The best move is to change the "Film Mode" to "Auto" or "On." For a blanket fix, go back to the main Picture menu, select the mode you use (like "Movie"), and turn "Auto Motion Plus" to "Off." Do this for each input (HDMI 1, Netflix app, etc.).
IF THAT DIDN'T WORK Some content, especially from built-in apps, might override your settings. Try enabling "Game Mode" for that input—it disables all processing, including motion smoothing. You can also try the "Film Maker Mode" from the quick settings menu, which is designed to turn off all post-processing.
HEADS UP Remember, these settings are saved per picture mode per input. If you switch from "Movie" to "Standard" mode, the motion settings will reset to aggressive defaults. Pick a mode you like, dial it in, and stick with it.