I recently installed Neon on a Surface Pro 3 tablet, and it works remarkably well, with a couple of caveats. One is that I can’t figure out how to consistently select items so that they can be dragged and dropped. For example, I’ve managed to drag addresses in Firefox onto the bookmarks toolbar a couple of times, but I’m not sure exactly what I did to make it work. Long-pressing on the address icon typically doesn’t select the item for dragging. (Drag selection is easy with a mouse.) Is there a consistent method for drag selection using the touchscreen in Neon, or does it vary with the application?
I also use kde on a touchscreen capable device. There are different case for selecting and dragging. For example Dolphin as a special selection mode, you trigger it by longpressing a file or directory, hitting space bar or also trough an icon wich can be added to the toolbar.
I think the selection/drag ui is more dependant of the app implementation. For example, text selection in chromium is the typical Android one, on firefox it is less reliable. On some apps you trigger by double tap and other by long tap.
If you don’t know in systemsettings > General behaviour there is a setting to activate touch mode (more padding for icons in the systray, more space in menus, …)
Note that I am sharing my experience as simple user. I don’t know much of the internal of touchscreen implementatin in kde. There as been quite some improvement recently with plasma6 and 6.3 bring some bugfix (there is a bug that trigger edit mode when switching virtual desktop with touch gesture, but only if desktop is configure to show files on the desktop directory).