I was gonna ask why so I could provide a counter argument, but then the question specifically asks for a movie you will never be convinced is good. So I won’t bother lol.
I gave them an updoot for answering the question even though my personal opinion is that the two new Dune movies are top 10 movies of all time.
Nothing appeals to everyone, and I dislike a lot of critically acclaimed movies and other media because while they just don't resonate with me. Top Gun Maverick was a mediocre retread of so many movies that came before it that while it was well executed from a technical perspective, I found it forgettable and don't understand the hype.
I have a hundred of top 10 movies, and I don't understand the hate for the new Dune movies. The actors are good, the movies stick to the script, the picture is pretty and the music is nice too. I was also pleasantly surprised that you could transpose all this world to a movie because it's kinda difficult. You can't please everyone though.
That goes for the main characters and the background characters imo. The second movie did a lot better in regard to showing off the different cultures but the first one just felt so...empty. People just did things and had things done to them, and I didn't understand why I was supposed to care about any of them.
Not the person you're replying to, but for my own POV:
I think the new Dune movies are the best they could be and I'm glad I was able to catch them in theaters, but they've also convinced me that Dune just isn't a franchise I'll ever be interested in. I'm not sure if I'd bother with the third movie, and any spin-offs are also fully out of the question for me.