[digiKam-users] Where do the pick widget "flag" icons come from?

[2895qgvg6v at liamekaens.com]

I've installed digikam (7.1) from the debian distribution, as well as cloned the current repo and built it locally, but when I run either version, I see empty boxes instead of the red, yellow, and green flags for the pick label widgets in both the filter tab in the right sidebar and the Picture Properties section of advanced search, and I also don't see the colored flags (just the accompanying text) in the labels view.  In https://invent.kde.org/graphics/digikam/-/blob/master/core/libs/widgets/metadata/labels/picklabelwidget.cpp#L255 I see lines like
            return QIcon::fromTheme(QLatin1String("flag-red"));
which it appears looks up the icon in current them.  I'm guessing its not finding these "flag" icons.  I don't see any messages about this in the console output, even after setting QT_LOGGING_RULES="digikam*=true".

I'm guessing that I'm missing some dependency, but I can't figure out what it is.  Can someone give me a hint where these "flag" icons are supposed to come from?

Thanks.