I used to use single-click, but now KDE 5.23 on my computer refuses to
accept that setting.

My root user account will allow single-click, but my ordinary user account
will not

If I ever find out how to force the single-click option in my user account, I'll do
that swiftly. But, for now, I'm forced to do the Microsoft Windows thing
and use double-click. I hate that I cannot use the single-click anymore. I wish
that I knew how to force it to work on my user profile.

Is there some text-file that can be edited that will allow single-click to work on
my computer running kernel 5.15.4 with KDE 5.23.3? Or, would someone tell
me how to troubleshoot my user profile to try fixing the single-click functionality?

Keltonix

System Settings -> Workspace -> Workspace Behavior, there you can set the desired option.

FWIW: default on my system is "Clicking files or folders Opens them" (details of my system in signature), if you have something else then blame your distribution