IIRC, the biggest issue with TrueNAS SCALE + Docker is that they really run the containers on a ‘hidden’ kubernetes cluster and obfuscate the standard docker and docker-compose way of doing things behind a gui with limited customization and poor field descriptions.
I found it much easier to spin up a VM on SCALE and run docker through that, although then you have to deal with multilayer networking.
… To be fair, this was when SCALE was still in beta, so it has possibly improved since then.