I wanted to try the arc icon theme but its packaging appears to be broken. The arc-icon-theme package requires moka-icon-theme, however that does not appear to be included. Official repositories only, AUR not enabled. Here is the log:
[mircea@linux-qz0r ~]$ sudo pacman -S arc-icon-theme
resolving dependencies...
warning: cannot resolve "moka-icon-theme", a dependency of "arc-icon-theme"
:: The following package cannot be upgraded due to unresolvable dependencies:
arc-icon-theme
:: Do you want to skip the above package for this upgrade? [y/N]
error: failed to prepare transaction (could not satisfy dependencies)
:: unable to satisfy dependency 'moka-icon-theme' required by arc-icon-theme
/edit: ah screw all that the package is called arc-maia-icon-theme now as the Manjaro variant as seen in the PKGBUILD, one would go with that.
/original: Hmm, yes looks like a contradiction, while arc-icon-theme is unfinished work dated from 2016, according to the author:
This theme doesn’t provide application icons, it needs another icon theme to inherit them. By default this theme will look for the Moka icon theme to get the missing icons. If Moka is not installed it will use the Gnome icon theme as fallback.[…]
But if you are on KDE there is no Gnome icon theme to fallback and the dependency was removed some time ago as seen in the PKGBUILD (and the servers), hence the error. (I guess one could install “moka” from the AUR but it’s not optimal)
So @Ste74 could enlighten us more I think (if he has any time) 
P.S. I’ve moved it back to packaging with-out- your permission 
, sounds more appropriate.