In the latest build Kodi 19 does not start (LibreELEC-RK3399.arm-9.80-devel-20191011115114-6e9040d-box.img) I think you forgot to link the libraries:
You took the version with kernel 5, this is a very new direction and a lot of things may not work from version to version. It is intended for General tests.
at the moment I don't know how to start the NanoPC-T4 from USB, so I haven't tested it yet.
See the posts in the topic. Verification is very simple. To write the image Armbian to SD card (do not need to configure DTB). The image on the SD card is only needed to run u-boot, then it should start from USB. Write to USB flash drive LE with kernel 4 (you can use any working version of LE). Configure on USB correctly DTB. Connect SD card and USB flash drive to T4. Turn on the power and wait 3-4 minutes. If nothing happens, you need to try to connect a USB flash drive to another connector USB. Start your tests with USB 2.0 connectors. I have on EDGE and on Magicsee N6 now in eMMC already installed the latest version of LE (20191011 with kernel 4) and now I can quickly run different test systems from a USB flash drive.
What is the difference between the images (desktop and normal) ?
Versions of Armbian called Desktop have an XFCE GUI. Default images are server images.