mbim-network is just a wrapper script for the mbimcli (in debian/ubuntu both are coming from libmbim-utils package)
when you run that you can see the commands it's actually executing under the hood. First is you run --query-subscriber-ready-status, if you don't, you're "unitialized" and can't proceed with anything else. then you attach to "packet service" and call the connect, and finally you get the issued ip details to set up your wwanX interface with. after that it just works, i even get a public ipv6 address which is really cool feature to have.
So to conclude, all in all, m75n is a really nice little computer yet keep in mind it's very low power, throttles easily if it gets hot. Far, far worse than m90n nano iot. Choose wisely. Because I got these for $150 each it was in okay range for performance. Expandability/upgradability is good(except for RAM and CPU lol). It was just luck, especially since both units were under 20 hours total run time according to their NVMe SMART data. And overall condition. Barely ever touched.