I installed KDE Plasma theme editor, changed the theme and replaced NetworkManager icons with those from oxygen theme, and it works much better on a dark theme. attached screenshot: openSUSEdark-test-icons-vpnconnected. Also attaching the edited theme, in case it is useful. Please note i changed the metadata.desktop description, as I am not part of openSUSE team and did not want to create any issue. I hope this is helpful Cheers Mauro