I am using nano version 2.2.6 and I have no idea why copying isn't working.
What I do now is cut and then paste it two times, but before, I was using Alt + 6
without problem, what happens¿? Thank you in advance
In my graphical desktop environment (i3 window manager), which "hosts" applications such as nano, nano's copy keyboard shortcut Alt+6 didn't work because I had previously set up i3 to use Alt as its own modifier key. With this configuration, pressing Alt+6 is interpreted and swallowed by i3 ("select i3 workspace/desktop 6") and never reaches nano.
The workaround of adding Shift to "escape" i3's keyboard interpretation also didn't work, as Shift+Alt+6 was also explicitly bound by i3 ("move current window/application to i3 workspace/desktop 6").
I solved this issue by changing i3's modifier key to Windows.
Since then, nano's copy keyboard shortcut Alt+6 works again and doesn't collide with i3's Windows+6.