I ended up working this out with the help of this post - specifically, if you add the following to /boot/armbianEnv.txt, you can force the video mode.   Some examples:   640x480 extraargs=drm_kms_helper.edid_firmware=HDMI-A-1:edid/640x480.bin video=HDMI-A-1:640x480-24@60   1080p extraargs=drm_kms_helper.edid_firmware=HDMI-A-1:edid/1920x1080.bin video=HDMI-A-1:1920x1080@60   I didn't have to install any extra packages or anything using Armbian Debian St