Armbian OS (Debian Linux) for Tinkerboard does not have 1280x800 resolution by default and I used 1280x720 for a while. Today I found very nice solution

  • Open terminal window, type
    cvt 1280 800
    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 "1920x1200_60.00"  193.25  1920 2056 2256 2592  1200 1203 1209 1245 -hsync +vsync
    Option "PreferredMode" "1920x1200_60.00"
    EndSection

  • Reboot Tinkerboard, new mode 1280x800 should appear in display settings.