The middle button paste may be set elsewhere. I'm using Ubuntu Gnome and there is an option for it in the gnome tweak tool. I think the default on install was off. It's "Middle-click Paste" and should be set to "ON"
There's probably lots of ways to set it, I do it through gnome tweak tool, which is a gui. I can't say for certain if this is available in lubuntu or xfce. On gnome, I search for "Tweak Tool" in applications or from a terminal window I can enter "gnome-tweak-tool" to launch it.
The setting for "Middle-click Paste" is under "Keyboard and Mouse" then the subheading "Mouse"
The middle button paste may be set elsewhere. I'm using Ubuntu Gnome and there is an option for it in the gnome tweak tool. I think the default on install was off. It's "Middle-click Paste" and should be set to "ON"
There's probably lots of ways to set it, I do it through gnome tweak tool, which is a gui. I can't say for certain if this is available in lubuntu or xfce. On gnome, I search for "Tweak Tool" in applications or from a terminal window I can enter "gnome-tweak-tool" to launch it.
The setting for "Middle-click Paste" is under "Keyboard and Mouse" then the subheading "Mouse"