I grew up thinking the Warner Bros. characters were the superior cartoon stars (and that Daffy is better than Bugs; my wife and I still argue about that). Disney is more like Apple...the people who like them really love them and get sucked into the rabbit-hole, but everyone else sees them as a cult.

In Scandinavia, the older generations mostly know these characters from comic magazines rather than the animated cartoons, as those was rarely shown on TV. The Disney magazines was called Donald Duck but also had stories with other Disney characters like Mickey Mouse, Goofy etc. If you ask a Scandinavian about Donald Duck or Mickey Mouse, they will most likely think of the comic magazine rather than the animation.

Disney artists like Carl Barks created new stories in a genre quite distinct from the animated cartoons. While the cartoons are mostly slapstick humor, the Barks stories were longer narratives where the characters went on various adventures. A lot of the stories were produced in Europe for the European market, since the magazines were never as popular in the US (where I believe superhero magazines were more popular, for whatever reason).

WB and Hanna-Barbera and other studios also tried to publish comic magazines, but didn't manage to adapt to the medium as successfully, so they are less well known.

Is it due to the US being prudes and Donald Duck doesn't wear any trousers/underwear?

I'll contribute another anecdotal data point; I've never known anyone even to consider that point of view. It's more that Donald Duck comic books just didn't catch on here the way they did in other countries. But people do recognize Huey, Dewey, and Louie.

No, most Americans don’t perceive him as naked, any more than they do Bugs Bunny or other anthro mascots.

I think it’s the accent. His voice actors are pretty hard to understand sometimes.

Interestingly, having only ever introduced to those characters through comics, I never pictured any particular accent and instead imagined them speaking normally.