Disable automatic/by default USB network sharing
Currently, at least on the PinePhone, USB network tethering is enabled automatically when the Mobian device is connected via USB.
On a (Fedora) host I connected to my phone, this resulted in an enabled "USB Ethernet" interface, which gained a higher priority than my wired NIC, causing all traffic to route via my phone.
Luckily in my case the phone was connected to a WLAN, so the problems this caused were limited to low throughput and high to very high latency on the host, but if the phone had been using mobile data, it could have been a much more expensive experience.
Disabling the interface on the connected host fixed it for that host, but users would need to know to do that, and also to manually do the same for every new host the Mobian device was connected to.