LXC/LXD vs Docker
Proxmox supports LXC, TrueNAS supports kubernates. The difference between LXC and docker container is, the LXC runs full OS without kernel, docker container only runs application.
Persistent docker container
Docker container also can be saved as image to be used next time. But the execution parameters can not be saved. To relaunch again, docker compose file can be a good choice if no change after container created.
LXC is persistent
LXC is a running VM sharing kernel and drivers with host, so OS and it's configue are in LXC.
The disadvantages of LXC are
Scaling is not at application level