Currently nm-tray is the only status icon that is dark over dark with papirus icon, making it difficult to see. That's because the icons it is using are the "symbolic". If icons are change to non-symbolic that will be solved. The only problem would be that when clicking the icon there appear a list of options with icons (like active connections) and that list has a light background and now, that the icons are light, they don't see well in that case. The text is dark so it can be read.
Final solution should be to change symbolic icons to none symbolic and make the colors (background and fonts) of the list change with the theme.
the icon names should be change in the file src/icons.cpp