After upgrading to KDE 6.6 on KDE Neon, the System Settings app no longer appears in the search box (either the Alt-Space search box or the Meta launcher)
The app still exists and can be run from the console or a dedicated quicklaunch shortcut, and individual preference panes show up in the search, but not the overall System Settings app.
I tried running kbuildsycoca6, balooctl6 check, apt install --reinstall systemsettings, and restarting my session but the app is still missing from search.