I am having a hard time getting the setup to require doubleclicking. I hate the single click. I found the article stating go into system settings → mouse and change to double click. I did that. Now I require a double click to open icons on my desktop. But if I open Dolphin to administer files, they still open with a single click. I’ve looked around dolphin settings and not finding anything to change it to double click.
I just noticed that when opening dolphin as non-root, it works fine. When I open dolphin as root, it’s a single click. Wonder if I need to login to the pc as root and change it to doubleclick the same way.
Ok, how do I login to the system as root? The login doesn’t give me an option to manually type a name. As well as in users, I don’t see root listed to make sure it’s able to login.
Try:
ALT+F2----type in “kdesu systemsettings5” without Quotes, enter your root Password in the next Window and change the settings for User root…
Figured it out I guess. I’ll leave the root dolphin as single click. I wasn’t using the non-root because previously it wasn’t displaying my second hard drive. Now the non-root Dolphin is showing me my second hard drive, so I’ll just use best practice and not use root access to my file system constantly.
Well settings like single and double click are a set by each user not the system and root is a user also so you would have to set the double click for root also.
I’m the opposite hate double click and always change any Windows to single click 
Remember that Linux is multi user and each user has their preferences stored in their home. BTW root’s home is /root. not in /home. This allows repairs when /home is not mounted
You should never log into a GUI as root in any case you can inadvertently damage things if you do. I have not logged on a GUI as root for years it is never needed