Who do you think should be the main villain for MCU's Fantastic Four? I don't think it will be Doom because he's already been the main villain in the previous films.
Fantastic Four
Maybe Mole Man, he was the 4's very first villain all the way back in issue #1
I totally agree with you! Dr. Doom is way too overused in previous Fantastic Four movies! I therefore propose a preview of Cillian Murphy in the role of Victor von Doom but for me, the perfect enemy would be the Mole Man! he has style, a mysterious side, good origins! He is stylish!
Then we can always look among the unknown and make a little more "cosmic" enemy like Anihilus, Molecule man, Super Skrull, the Terrifics (or even why, not a good version of Galactus preset as a celeste in the Eternals!) .
since Immortus exists, they could introduce the evil variant Kang, I mean it seems obvious
So we can leave Victor Von Doom for the second or third movie, as this villain has already appeared directly in the previous Fantastic Four movies.