So I've played with TrueNAS Scale in a VM and I can understand your frustration. Following the installer is easy, but once it's up and running nothing is easy and nothing just works. I can very much see why typical home users would prefer the ugly unRAID WebUI.

Launching a container via the WebUI doesn't work because gets stuck indefinitely at "Deploying" even thought event log clearly shows
ErrImagePull. Can't check logs because the WebUI fails with Error Code 400 every time. It's a very clunky experience. I'm not sure if the
docker command via
Shell is even supposed to work, but at least it can pull the image, so it's not a fundamental network error.

Can't use named volumes by design:
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docker: Error response from daemon: invalid volume specification: 'data:/data': 'data' 'path' not allowed to be mounted.

Can't mount host paths into the container by design:
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docker: Error response from daemon: invalid volume specification: '/mnt/pool1/dataset1/share:/volume1': Invalid mount '/mnt/pool1/dataset1/share' path. Following service(s) use this path: SMB Share.

Can't use default port 5454 by design. TrueNAS wants you to use port 9000 or above.

After managing to run the container from the command-line without volume mounts, networking inside the container also doesn't work:
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SEVERE: Unable to set localhost. This prevents creation of a GUID. Cause was: 51bbe6f9e4b6: 51bbe6f9e4b6: Temporary failure in name resolution
So after 3 hours I was unable to run FileBot in a meaningful way. Renaming files / selecting a license file / pretty much anything that FileBot does would require access to the SMB file system where our files are, and internet access. I don't even know where to start with the network errors. Also wasn't able to connect remotely to the Xpra WebUI even though it seems to be running according to the console output. Probably another symptom of docker containers not having network access by default.
tl;dr
docker on TrueNAS doesn't work like
docker on any other Linux platform, so you will probably need to spend a lot of time in the TrueNAS support forums to understand how TrueNAS does
docker.
EDIT:
The example configuration in this thread might help you though, seems to work for other users at least:
viewtopic.php?t=13865