Looking at their assorted instructions I see some pre-canned methods that assume a specific OS. I can't find detailed instructions for people that already have Node, FFmpeg and MariaDB installed. Is that on a forum?

How have you found Shinobi versus Zoneminder? I've been using ZoneMinder for years. It's a bit clunky but once it's set up it works fairly well, but I'd be open to switching to something better.