@20-100 To install NetBSD for another aarch64 than the RPI by building the image yourself you'll first need to install a board-specific U-Boot and also make sure that the DTB files are in place. There is a guide for the ODROID-C1 at https://wiki.netbsd.org/ports/evbarm/odroid-c1 and I guess the process would be almost identical for the C2.
However this is what Jared already has done for us, all his images are pre-built with a board-specific U-Boot and the right DTB files - so images from https://www.armbsd.org should work out of the box. Have you tried both the NetBSD 9 and current ODROID-C2 image from Jared on different SD cards?
If you're considering a new SBC from Pine64 I would highly recommend the RockPro64. Runs like a charm on NetBSD. Although there still isn't any drivers for the GPU yet, it's in the works and Panfrost/lima drivers for the Mali GPUs will hopefully get released soon. The RK3399 CPU alone handles 1080p video playback smoothly (not fullscreen) with bearable screen tearing.
pfr I remember reading an older post from you mentioning that you maybe were considering getting the PineBook Pro or RockPro64 as a secondary NetBSD machine. Depending on your work style, I really recommend both of them. I'm using both the PBP and RockPro64 as my dailly drivers and have done so for awhile so feel free to ask me anything.
To anyone considering the RockPro64, go with the 4GB model. I thought 2GB would suffice but my memory runs out on Firefox 80 with 4-5 tabs open which is OK but leaves much to be desired..