I'm having the same issue and am still fighting for a breakthrough. I've been a tentative user of Linux systems for years and can't seem to progress from a noob state much. I'd like to argue that this is a wider issue of design, which has never had humans at its center, but what's the use. I'll just quote Don Norman and say "there is no stupid users, there is just bad design", and let's leave it at that. Anyhow, it's a fight each and every time so please point out if I got something wrong.
Generally speaking, the problem stems from he fact that the jail is running an isolated (?) set of credentials. The process of adding a mount point involves a boolean that says "Read Only".
One would be led to believe that if this is left unchecked, the root user of the jail will have write access to the mounted location or something like that.
Nope.
In order to gain write access there is an arcane workflow that needs to be understood and followed (
https://www.truenas.com/docs/core/coretutorials/jailspluginsvms/jails/settingupjailstorage/ starting at "Here is the typical workflow for adding jail storage:").
Setting a mount point automagically provides a read-only level of access, regardless of the said option. How does it make sense to provide read but not write access is beyond me. What I am trying to say is that this is a design flaw: it would make more sense and it would be obvious that permissions need this additional workflow if the simple setting up the mount point didn't give read access, none at all. The way this works now is misleading, and the "Read-Only" option displayed is a sadistic joke.
That said...
Following the workflow, I can verify that the plugin installation indeed results with a jail which contains a group and a user both named qbittorrent. There workflow says to create a username with the same name in TrueNAS and assign the user/group rights to the dataset. It doesn't say how and why mere naming of a user, that could be purely coincidental for that matter, can result in the jail user having the same rights as the TrueNAS user. That's something for the Linux experts to explain. Anyhow, I did just that, and of course, it doesn't work.
I fight on...
