It really does feel like their setup process is broken! Also, they fortunately only seem to break every 6ish months or so, which isn’t a lot but it’s really not great either. Maybe since it’s a newer one it’ll break less for the person you set it up for!
Why would your Jellyfin traffic need to go over the Internet if it’s on your local network? You should be able to install the Jellyfin app on your smart TV/Roku/etc or use the web client from a computer, point it at the Jellyfin local IP address, and view it over your LAN.
I’m using Zoho. It’s pretty cheap and wasn’t hard to set up with my domain.