Attempting to drag an app from the menu to the panel using a touchscreen doesn't show any sort of feedback indicating you managed to "grab" the app you want. It doesn't matter if it's from a grid or a list.
Drag-and-drop is actually totally broken on master right now. :( Wayland or X11?
Wayland. I can confirm it is totally broken on X11, but on Wayland it works, albeit without feedback.
Can reproduce. Operating System: KDE neon Unstable Edition KDE Plasma Version: 5.24.80 KDE Frameworks Version: 5.92.0 Qt Version: 5.15.3 Graphics Platform: Wayland