I sense I perhaps missed something important about how this all ties together.
Are we saying that if I don't have an internet connection on the network the NAS is on, then I do not have access to HexOS, so my locally running NAS loses that side of things and may as well be just running TrueNAS on it's own?
I mistakenly assumed that the HexOS system/portal was accessible from the NAS it self, and the online component was an optional extra thing I could use...