Hello there,
following this Guide to reflash SPI, I just flashed the RebornOS-ARM-rock5b-2023-01-22.img to my nvme and rebooted → 
Usually using Armbian (limited to Debian/Ubuntu) on my ARM SBC’s it is a very welcome addition to get ARCH on this board. I was planning to copy root fs, change extlinux.conf etc … the stumpled upon the Wiki 
Thank you, works very well so far.