amatwkgs [1] filed a deletion request for heif-gimp-plugin [2]: gimp 2.10 in [Extra] repository already has heif support, so this package is probably no longer useful.
[1] https://aur.archlinux.org/account/amatwkgs/ [2] https://aur.archlinux.org/pkgbase/heif-gimp-plugin/
