Clicking on the button do open the settings window from the Window Decoration KCM just does nothing now.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/1232
Git commit 050b4945cefaf0d7a4bde36f0eeadd4045499f7d by Nicolas Fella. Committed on 10/08/2021 at 10:14. Pushed by nicolasfella into branch 'master'. [kcms/decoration] Try loading decoration KCMs without plugin keyword We're porting away from using plugin keywords (and have done that for the breeze and oxygen decoration). However to allow that we need to adjust the loading code. Keep the old codepath for compatibility. M +9 -1 src/kcmkwin/kwindecoration/declarative-plugin/previewbridge.cpp https://invent.kde.org/plasma/kwin/commit/050b4945cefaf0d7a4bde36f0eeadd4045499f7d