MarsSeed [1] filed a deletion request for mergerfs-git [2]: Unmaintained VCS package since at least 2019, as per unanswered packaging fix request mentioned in comment.
AUR has a stable, maintained mergerfs package. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/mergerfs-git/
