CTL-V is the “MSWindows compatibility keystroke combination.”
It should work, but someone else posted about this not working for him also this past week.
Recommend trying the “original Linux” keystroke combo, CTL-INSERT.
Like I said in my original post, using the right click context menu doesn’t work either (Right Click, Paste).
I moved my .config, and .local directory out of the way, and it worked again for a while.
Then I started copying back in from the old config/local certain directories (nothing to do with KDE/Plasma, I did however copy back in gtk directories) and it broke again.
Edit: Klipper sees the copied item, but I just can’t paste it anywhere (with either keyboard shortcut SHIFT-CTRL-V for Konsole, or right context menu of paste in Konsole, or Kate, or any other application). It’s like Paste is disabled.
The Linux keystroke combinations should work at a lower and different level, so should generally be unaffected by any functionality like mouse button clicks in a Desktop environment.