Open KDE settings... set mouse to doubleclick to open application. Dolphin honors it. KDE desktop doesn't. Expected behavior: KDE desktop: doubleclick chrome icon should open ONE instance of Gooogle Chrome. Not TWO. Don't spin it. Just accept it as a bug.
The reason why you would want to require two clicks to open a file or folder is so you can select it first--because there are many things you can do with a selected file or folder. There are other things that cannot be selected, or that have no plausible actions you could apply to them if they were selectable. An example is a toolbar button. You don't want to have to double-click those, do you? Of course not, because after the first click selects it, there's nothing you could do with it, so that click is pointless. So the principle is this: when something can be selected because there are actions you can perform on it once it's selected, it should honor the single/double click setting. If an item can only be executed or opened, it should do that on a single click. App launchers in your Panel or the Application Launcher menu are not selectable, and even if they were, there's nothing you could do with a selected icon. Therefore, it does not make sense for them to honor the single/double click setting.
Hello Nate. Thank you for the explanation. BUT: KDE DESKTOP = Icons on the desktop: not buttons on a task bar. SO: one would expect it to behave the same as ICONS within Dolphin. Though it seems the icons on the desktop behaves like a task-bar, not a desktop. I DID find a work-around: remove all the icons from the desktop, add widget FOLDER VIEW. Drag icons from your favorites, drop it in the folder view. Conclusion: Then it works as expected. You click once to select it, right-click to have several actions, and double-click to launch it (it honors the settings!). One can even drag a box around several icons to multi-select, and one can control-click or shift-click to select many at once or deselect some. Am pretty sure 67.5% of all KDE users expect a Desktop to behave like a desktop, and if one sets Setting: Double-click: then a true desktop would honor its setting. Makes sense. Hope this work-around helps some other people.
Ah, I see what you mean now: when the desktop is in Desktop mode rather than Folder View mode, any icons you add to the desktop behave more like launchers on the panel (which always require a single click) rather than files, folders, and launchers in Dolphin) which respect the click setting. The reason for this is the same as what I explained before: in Desktop mode, any app launchers that you add to the Desktop are just like launchers in your Panel: they exist purely to be clicked on to launch the app, not so that they can be manipulated in any way. Think about it: if these icons require a double-click, what could you do with them after selecting them with only a single click? If you want double-clickable launchers on the desktop, the solution is to use Folder View, as you've discovered. Folder View is the default setting in recent versions of Plasma, so the Desktop now behaves like the majority of KDE users expect it to.