mirco [1] filed a deletion request for xdg-app [2]: xdg-app upstream has been renamed to flatpak, which is now in [extra]. I've written a notice of the name change in the comments a week ago so users can update manually. Imo, it should now be deleted.
[1] https://aur.archlinux.org/account/mirco/ [2] https://aur.archlinux.org/pkgbase/xdg-app/
