I am on the default KDE layout, and when I use the default application launcher (Kickoff launcher), it shows me my browser history, files in my system, and suggestions like “Get Software…”. How do I disable all of these?
Search for “plasma search” in your language.
You will come to a systemsettings page where you can enable or disable modules.
The Browser history only works via the KDE Plasma integration Addon in Firefox. So disabling the module in systemsettings is enough, but uninstalling the addon from Firefox would also do it (but not as cleanly as the module would always search and get no data)