This information is now outdated. I was not able to get any images running 5.4 kernels to work, but images with the 4.4 kernel work just fine.
I was only able to get one Ubuntu/Debian image out of all of them from the Rock64 wiki to work, and it was a minimal Debian image with a kernel tailored for media uses. According to what I saw on the forums, I'm not the only person with this issue. Big thanks to @mrfixit2001 for making that one working image available.
This is the process I went through to get things to work.
- Download the RockPro64 image from here.
- Use Etcher or the xz command to write that to an (>=4 GB) SD card. Note that the Rock64 boards are known to be finicky about SD cards.