xarchiver does not require GTK+3, however the Gentoo ebuild forces GTK+3. I suggest to change the GTK RDEPEND from x11-libs/gtk+:3= to >=x11-libs/gtk+-2.24 to fit in the existing XFCE 4.12 (xarchiver's "natural" environment) which is still based on GTK+2 . Reproducible: Always
Xfce is moving towards GTK+3, and we're not going to put any effort into supporting GTK+2 for a few more months.