This icon theme inherits from Adwaita. It is not a full icon theme but rather an add-on for Adwaita fixing missing icons that are used in Xfce. Icons used are designed from scratch or borrowed from Adwaita upstream or other non-affiliated projects.
Clone this repository and place the content in $HOME/.local/icons or /usr/share/icons
Select openSUSE-xfce in Xfce Settings > Appearance > Icons