It seems that Disney finally released an actual Windows app for Disney+. Theres no debug menu or anything anymore, so I cant see for sure what resolution it is, but comparing It with the browser version, its definitely higher resolution. I would say at least 1080p.
https://www.reddit.com/r/DisneyPlus/comments/lyaszh/disneyplus_does_not_offer_1080p_or_higher/

