I've tested the How-To, with the lastest Pi-hole Docker. (About 2 weeks old.) As a result, you might have noticed that --cap-add=NET_ADMIN has been added to extra arguments. However, if running Pi-hole in a Docker with a separate IP address (which is one of the very few ways to run it in on OMV and get full page blocks), the environment variable --dns=127.0.0.1 is questionable.
Again, I've tested the How-To as it is currently written. Since I'm moving right now, I don't have everything needed (at the moment) to test this, again, on real hardware. (I'll come back to this in a few days.)
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Regarding the password:
I believe if you check the container, with the modify button, you'll find that your password environment variable didn't take.