DebugPoint published a tutorial about enabling Legacy Kickoff Menu in KDE Plasma 5.21.
How to Enable Legacy Kickoff Menu in KDE Plasma 5.21
This quick guide explains the steps to enable Legacy Kickoff Menu in KDE Plasma 5.21. KDE Plasma 5.21 was recently released with many new features and improvements across the desktop. One of the crucial changes in the main application launcher. The application launcher was completely redesigned from its earlier iterations.