I altered the fantastic Papirus icon theme https://github.com/PapirusDevelopmentTeam/papirus-icon-theme (e.g. the places icons are orange now etc.) And other small changes. But in order to work 100% on KDE you need to install the icon themes Papirus-Colors https://www.opendesktop.org/p/1197105/ and Papirus-Light-Color https://www.opendesktop.org/p/1197109/ too. Only then KDE can do its full magic with the icon theme.