Those are the actors who played Duncan Idaho in the David Lynch adaptation and in the two Syfy miniseries. So, yeah, it's not wrong, just incomplete — though I have no idea why it only serves up those three. There's certainly no limitation to three images, as can be verified by searching for "Sherlock Holmes actor" or the like.

The result is still correct. There are multiple movies, therefore multiple actors which played the role of Duncan. If you are looking for an actor of a specific movie it usually helps to input also the year of the release.

It has been for a while. Never a better time to switch to something different

the other three aren't wrong, it's just an incomplete list.

my ddg default gave me the fictional character's wikipedia article as the top result (it lists all of them and what title they were in).

a vanity fair article praising momoa's work in the 2021 film was second, followed by the dune wiki character page and then imdb's 2021 film page was fourth.

i also have firefox keywords to search the wiki or imdb directly if i choose to, and that's what i would have normally done here.

Dune the wrong thing