Don’t forget; Up Up, Down Down, Left Right, Left Right, B, A, B, A, Select, Start.
To be fair, the double reboot trick does work if your car has been cleared/queued to receive the update but for whatever reason it’s not “phoned home” even while connected via WiFi. After rebooting, the car “phones home” and starts downloading. So it’s basically a way to force a connection. But this has no affect on whether your car has been cleared/queued for the update.