The default Plasma 6 clipboard is wl-clipboard. Klipper is 3D-printer firmware. You might still have one of the x-org clipboards installed: xclip or xorg-xclipboard.
My system setup is pretty basic though - no 32-bit libraries/apps, and I don’t think anything I use runs under Xwayland, so I don’t need any x-org clipboards.
Just a second - I just opened my clipboard settings from the system tray. I think you might need to uncheck the “Keep the selection and clipboard the same” box, although I just checked that box on my desktop & still couldn’t reproduce the issue.
Edit: Making sure the clipboard is set to only save in history when explicitly copied may also fix the problem.