I use the one-time email, on a VPN, but there’s no way around it transmitting your serial number. To keep it private in the future you need a dedicated offline mobile device to run the app, which after installing the app never goes back online.

I don't want to have an offline DJI-only phone.

Most people who fly drones are sending their IP, gps data, and serial number to DJI on every flight.

Yikes! I had forgotten all of that... maybe an old phone without a SIM might be a good idea.

An excuse to eventually brick your device.