ok, looks like I finally got it running.
Turns out it was a simple line I needed to add to the yaml volumes:
- /home/umbrel/umbrel/app-data/bitcoin/data/app:/data/app. (I added this line and it made it work)
Thanks for listening. Once it syncs I plan on migrating to knots, but this is fantastic!
Fun times, at least I'm learning something along the way, too.
Bitcoin kicks ass! (as we all know here, 😂)