Thanks for this placeholder but I decided to create a new thread myself. You can find it here: Linux Jails (sandboxes / containers) with Jailmaker Let’s continue the conversation over there and perhaps lock this thread? 
I put it under Apps and Virtualization because the Sandboxes documentation on the TrueNAS website is also under Apps:
24.04 (Dragonfish)/SCALE Tutorials/Apps/Sandboxes (Jail-like Containers)