10. Iron Man nanotech suit
While the technology present in Tony Stark's armors rapidly advanced in the MCU with every subsequent project, the special effects needed to bring the hero to life on the big screen seemed to have regressed. Now, don't get me wrong, the design of the suits themselves is breathtaking and a great adaptation of their comic book counterparts. But while the Mark-lll armor in Iron Man 1 was a mixture of CGI with practical effects, Marvel opted to go full-CGI for the nanotech suit in Avengers: Endgame (perhaps to make things easier for themselves in terms of production), and it unfortunately shows.
The problem with Iron Man's nanotech armor is similar to Tom Holland's Spider-Man costume in Homecoming. The armor is too smooth for it to look real. There are no scratches on the metal, nor tonal changes in its paint.
Since a real-life nanotech suit hasn't been created yet in our world, we don't know exactly what it would look like. Perhaps the MCU does have a realistic depiction of it, and we just don't know it yet. But right now, the only reference we have is real metal, which doesn't look this way in the slightest. Maybe that's why it's so easy for our brains to tell the Nanotech suit was made on a computer, as opposed to the Mark-lll armor.
9. She Hulk
Let's start by clarifying She Hulk's animations in Disney Plus series She-Hulk: Attorney At Law are actually pretty great. Her facial expressions manage to faithfully capture Tatiana Maslany's outstanding performance and also sell you on the idea that this could be a real character living in the MCU. However, one of the main problems with She Hulk's CGI is the tone of green in her skin. It's too saturated and pops out way more than Bruce Banner's. Besides, her skin also lacks key details such as pores in a lot of shots, giving her an overall unrealistic look.
It's also perplexing how She Hulk's budget is 225 million dollars, five million dollars more than the one used for the first Avengers movie, and the VFX is arguably worse. Granted, the Avengers runtime is shorter compared to all of She Hulk's episodes combined (about an hour and a half shorter, to be precise). That means there are more CGI shots in Jennifer Walters' series than in Earth's Mightiest Heroes' big screen debut. However, She-Hulk had fewer protagonists and was released 10 years later, so by all means it should be at least of the same level of quality as the Avengers, and that's just not the case.