Which Nvidia box? A Shield? What are its specs?
Which Samsung TV, or what are its specs? (60Hz, 120Hz, 240Hz for example)
I assume when you say iPTV you’re using an app to connect to a service. Do you have any info on its specs?
In any case, the soap opera effect is caused by motion interpolation (usually software in the device made to adjust a lower frame rate into a higher frame rate.)
“Soap opera effect is consumer lingo for a visual effect caused by motion interpolation, a process that high definition televisions use to display content at a higher refresh rate than the original source.”
To try and figure it out, you’re going to need to disable the interpolation, but you first need to find it. Start with your TV. Does it have a Game mode? Try using that mode. Otherwise, try looking for settings related to motion interpolation. The linked articles have some ideas.
I believe the Nvidia Shield also has some AI scaling enhancement. This may or may not have an effect, so you may need to play with that.