It used to be that if you opened Kirigami Gallery via the CLI, it displayed the material style, but if you opened it from KRunner or a Plasma launcher, it used the Breeze style. This doesn't happen anymore; now it always uses the Material style no matter how it's launched. See also Bug 403659.
Workaround: run `QT_QUICK_CONTROLS_STYLE=org.kde.desktop kirigami2gallery` from the command line.
*** This bug has been marked as a duplicate of bug 403398 ***