Did you notice the post-install messages about the randomly generated first-time password?
If not, re-install the "qbittorrent-nox" package again, and pay attention to the messages on your screen.
(Please don't use a "Plugin". Use a manually created jail.)
Thank you for the suggestion.
I re-installed the plugin a couple of times and it doesn't appear to output a first-time password anywhere.
I am not sure what you mean by not using the plugin, that's probably because I am not the most experienced with plugins/jails.
However, as I was desperate to get the system up and running last night I updated my CORE version to SCALE, which gives you the ability to open logs for each app.
I managed to find the first time password in the logs and now everything is up and running.
I am not quite sure why the log functionality is missing from TrueNAS CORE (or at least not easily accessible for beginners), it seem to me that this should be an essential feature.
If anyone else is struggling with the same issue, and planning to do the upgrade to SCALE please note that you will need to reconfigure the POOL and your plugins/jails. At least that's what the warning highlighted when I updated mine. As my pool was pretty much empty it did not matter to me, but if you have a lot of data I am not sure how it would affect that.