I have got it to boot now, off uSD. I had to enable maskrom mode and remove my nvme disk. I get a (full HD) HDMI display but unfortunately its cropped and doesn’t quite fit so I cannot see the whole of the bottom row of text ie the command line itself and so I can only really use its terminal via ssh or UART unless I type blind.
I’ve not tried installing it yet - I’m mainly interested to see if FreeBSD can utilise the full speed of the NVME interface ie PCIe 2.0 speeds. If the FreeBSD devs can get 4K output and the wifi working then I might consider switching from Manjaro.
Cool to see a BSD booting on the RockPi4!