I actually started using HomeAssistant on TrueNAS Core a few years ago. From my understanding the best way to do this now it's to use the TrueNAS X86-64 ISO in a VM. The TrueNAS docker system seems to be integrated differently than a standard docker installation on an os like Debian.
If you really want to keep using docker on TrueNAS you should create users with unique ID's in TrueNAS and give them permission to access the needed resources. Those ID's also need to match the user in the Docker container.
I personally use HomeAssistant on an Odroid N2+ and haven't made the switch to TrueNAS Scale so I can't be much help beyond that.