After installing elementary OS Loki on my laptop (Lenovo Flex 3), when I press towards the middle of the click bar on my touchpad, it will copy or paste depending on the location. I've gone into Mouse & Touchpad settings and changing the physical click setting can disable copy and paste but also takes away my ability to "right click" with the right side of the click bar. I want to be able to right click using my touchpad but this copy and paste has to go. Any suggestions?
I also used the xmodmap solution, but this disables the middle mouse completely. Another solution is installing the gnome-tweak-tool from the AppCenter and disabling Middle-click Paste: https://askubuntu.com/a/872165/519324
I opened an issue for this. As of elementary OS 5 and 5.1, it has been resolved and there is now a toggle in System Settings → Mouse & Touchpad → Clicking called Middle click paste that can enable or disable this behavior.