pklaffert had the right idea, but the problem are the internals of the MultiResolutionImage component. It is an Item with an Image as child, so setting the antialiasing property doesn’t affect the Image. As a workaround you can access the antialiasing property of the internal image by adding image.antialiasing: true to the MultiResolutionImage. (you can ignore the warning of QtCreator that imagehas no members, this is just an autocompletion issue of the editor)
We will change the internal image to inherit the antialiasing property of it’s internal Item parent with the next update.