Klaus was great. So were How to Train Your Dragon: The Hidden World, Missing Link and Toy Story 4. Haven't watched I Lost My Body yet. But it was a great year for animated movies and any one of them could have won.
Toy Story 4 is brilliantly animated but not just that, it brought certain cinematography techniques normally used in film to animation for the first time (see:
https://nofilmschool.com/toy-story-4-pixar-cinematography) and thus moved the field forward. In this light I see it as similar to Spider-Man: Into the Spiderverse, which also brought "new" to the field of animation. That the movie managed to have a good story that changed the life of a main character in ways the previous movies did not, when the series seemed wrapped up neatly after 3, helped.
In a *very* tough field, I wouldn't have begrudged any of them winning (aside from I Lost My Body but only because I haven't seen it), and I'm absolutely fine with TS4 getting the win.