Didn’t see it mentioned here but check out Keep Alive.

https://f-droid.org/packages/io.keepalive.android/

You should be able to make docker exempt from early oom. Check it’s github for instructions.

You could always try tailscale until you figure something else out. Its not really self hosting but its better than having everything accessible to the public internet. Set it up in browser and follow their set up guide then install tailscale app on Truenas and whatever other device you plan on using it with.

Classic Disk Destroyer moment.