Armbian OS (Debian Linux) for Tinkerboard does not have 1368x768 resolution by default and I used 1280x720 for a while. Today I found very nice solution

  • Open terminal window, type
    cvt 1368 768
    This should give you the modeline values to put into:
    /etc/X11/xorg.conf.d/20-modesetting.conf
  •  Then add

    Section "Monitor"
    Identifier "HDMI-1"
    Modeline "1368x768_60.00"   85.25  1368 1440 1576 1784  768 771 781 798 -hsync +vsync
    Option "PreferredMode" "1368x768_60.00"
    EndSection

  • Reboot Tinkerboard, new mode 1368x768 should appear in display settings.