I’m sorry it’s under difficult circumstances, however. I’m not an expert with regard to these questions but I’ll try to help.
I believe it is indeed related to the relative old age of our current ISO installer, unfortunately, but I’ve seen this error in the past. I believe you have too, as you mentioned having poked around the forum further. I would point you to a few instances where users had the same error on similar hardware (Ryzen & NVMe drive):
You may have seen them already but maybe they’ll help.
As mentioned above, I’m not expert on this but I too would look into using a separate machine to install Rockstor onto the NVMe and then transfer it into the final machine. @Haioken and @phillxnet will know a lot more about it than I do, but if you have the ability to try that easily it might be worth it.
@phillxnet will, again, be the reference there, but I do believe so, yes. This will, most likely, improve compatibility with new hardware like that immensely.