yochananmarqos [1] filed a deletion request for gnome-cosmic-git [2]: Abandoned and never was packaged properly. The dependencies are incorrect and the maintainer never responded to comments.
Either way, System76 is no longer actively maintaining this as they're working on the new Rust based Cosmic desktop. [1] https://aur.archlinux.org/account/yochananmarqos/ [2] https://aur.archlinux.org/pkgbase/gnome-cosmic-git/
