Am I to understand that there is no way to simply plug in an NTFS-formatted, EXT4, etc (temporarily, not permanently) drive with data on it for the purposes of transferring the data to the TrueNAS machine, and that I must only achieve data migration using something like rsync or network-based transfers (SMB/NFS)?
Clearly, there has to be a more efficient way than this.
While more efficient, coping files from foreign file systems has trouble with properly coping owner, group and file attributes properly. iX removed this feature because of those issues.
Access from SMB or NFS forces the files to use whatever owner, group and file attributes the sending computer has. (And are allowed by the NAS’ share…)