"Double click to open files and folders (select icons on first click)" is selected in my mouse_kcm. However an icon added to my desktop when I drag it from the apps menu (kicker) to my desktop and I select "Add icon" option in pop-up menu is opened on single click. Trash and Home icons respect my setting in mouse_kcm and are opened on double click.
Can reproduce also on Wayland Operating System: KDE neon Developer Edition KDE Plasma Version: 5.14.80 Qt Version: 5.11.1 KDE Frameworks Version: 5.51.0
This was decided against, see discussion in the linked bug report. *** This bug has been marked as a duplicate of bug 348960 ***