j'ai réussi à créer la résolution comme dans le tuto
seemax@Seemax-dev:~$ xrandr
Screen 0: minimum 320 x 200, current 1024 x 768, maximum 16384 x 16384
HDMI-1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 304mm x 228mm
1280x1024_60.00 60.00 +
1024x768 60.00 + 75.03* 70.07
1920x1080 60.00 59.94
1280x720 60.00 59.94
832x624 74.55
800x600 72.19 75.00 60.32 56.25
640x480 75.00 72.81 66.67 60.00 59.94
720x400 70.08
seemax@Seemax-dev:~$