Thanks god I solved it!!!
While exiting from /etc/lightdm/lightdm.conf I pressed inadvertently option+x instead control+x and I added “†” in the file without realising it.
Thank you guys for helping me out

@sean I cannot start magic mirror using npm start dev because it’s like the graphical environment didn’t load.
My config file is ok, I just checked it

Guys I’m becoming mad, I have spent last two days configuring my smart mirror with google assistant, Spotify and other. Finally today everything was working more or less (just minor adjustment to be done).
Unfortunately now it doesn’t work anymore, it doesn’t even boot. I can guarantee that before booting I changed just two things:

• I removed this line
  display_rotate=1
  from
  /boot/config.txt
• I removed
  -nocursor
  from
  xserver-command=X -s 0 -dpms -nocursor
  in
  /etc/lightdm/lightdm.conf

Here is a screenshot:

All I get now is this:

Lorenzo