The actor published a photo from the set on his Instagram account, and this shot speaks more than it seems at first glance.
In the photo, he sits by a trailer—grayed, with a book in hand, and behind him is a poster featuring Doctor Doom.
And if you thought, "Wait, is he playing a villain now?" — yes, that's right. For those who missed it, in "Avengers: Doomsday" Downey will first appear in this role, as Marvel Studios announced in March 2025.

Source:
@robertdowneyjr
Robert wrote under the photo that the memoirs are "very instructive." But personally, I think it's a kind of hint at a possible clash between Doctor Doom and Renner's character, Hawkeye, in the upcoming blockbuster.
Also, if you look closely, you can see characteristic black markers for motion capture on Downey's face. What could this mean? It's very likely that Doom's mask—the iconic, face-covering one—will be digital this time. Or perhaps graphics will be used to add scars to Robert's face, as in the comics.

Source:
imdb.com
We'll find out the true version very soon. The premiere of "Avengers: Doomsday" is scheduled for May 1, 2026. Earlier, we at zoomboola.com detailed which actors and characters will appear in the new part of the superhero franchise.