System Settings > Desktop Behavior > Workspace

Given the menu path above, under Click behavior, I enabled the radio button "Double click to open files and folders (single click to select).
I added "System Settings" and "KSysGuard" to the Desktop, but it takes only a single-click to open them.
I know about the Tweak to Press and hold to reveal their handles. That works.
It doesn't seem to matter if the Layout is Folder View or Desktop Containment.

It depends on how you create the links. I assume you are dragging it from the menu. If you add it as an icon then it acts like a launcher and not a file/folder, hence the single click. If you add choose either the Link Here or Copy Here options then it will act like a file/folder and be activated by a double click. Hope that helps.

If you have two VGAs, try disabling one in BIOS, and running all your monitors through the one card.

This post is very similar to my experiences, along with some other posts.

- Can't double-click title-bar to make window full screen
- Can't double-click icons on desktop to open, but can double click icons in dolphin (KDE set to open with double-click).

Sometimes rebooting fixed. Always "kwin --replace &" fixed until next reboot. Often, changing from double click to single click and back again fixed it, sometimes caused it??

I went with a gut instinct and I think in my case, issue caused by two VGA cards, one monitor attached VGA to onboard Intel HD4600 and other Display-Port to NVidia GTX970. I bought a DVI to VGA adapter so I could run both monitors through NVidia. I disabled Intel VGA in the BIOS. That done, I got no display through the DVI-VGA connection, not obvious in any way what to do to trouble-shoot that so I reloaded my system and now it all works. It was no problem reloading my system since I had been distro-hopping earlier in the week. I did discover whilst distro-hopping that I still dislike GNome .