Modified title to reflect that USB-based tethering, as I’m now able to do from my phone, would also be adequate. Huh, turns out “Ethernet” is the protocol, not the physical connector, so it’s still Ethernet either way. Anyway, this looks like it’s essentially my question but for USB, and it looks like it goes to some effort to overcome hardware quirks, where the solutions may be Pi4-specific. So using the actual Ethernet port is sounding like a preferable solution anyway.