I've gone through Adobe Stock to find some nice assets with a transparent background, and added them all to a Library.
In Illustrator all the thumbnails have a transparent background. Before licensing them I've added a few to my composition and they have a transparent background.
However when I click the shopping cart icon to license them Illustrator downloads the JPEG and not the PNG version.
Where do I find the option to choose PNG?
Not all assets have the PNG option. Adobe only recently added PNG as an option, in addition to JPEG. Please post the asset id, and I can check.