In theory: 1. Wait until you enable the cellular again 2. push an update to the baseband firmware 3. when you disconnect, the new firmware will tell the OS that the baseband is disconnect, in reality, it's doing nasty stuff.
You'd only notice it due to the battery draw.
You need burner phones to cycle after each usage.
TBH, seems you cranked up the paranoia to 11. The VPN has to terminate somewhere, so if I was a state actor attacking you, I'd figure out where that is. WiFi+BT firmware isn't bullet proof, either, and hypothetically an exploit chain could be found to enter via WiFi and stealthy enable cellular. In practice XKCD #538 applies: https://xkcd.com/538/
For most of us the attacker is someone trying to make some money by scamming, stealing CC or installing a malicious app.
You need burner phones to cycle after each usage.
TBH, seems you cranked up the paranoia to 11. The VPN has to terminate somewhere, so if I was a state actor attacking you, I'd figure out where that is. WiFi+BT firmware isn't bullet proof, either, and hypothetically an exploit chain could be found to enter via WiFi and stealthy enable cellular. In practice XKCD #538 applies: https://xkcd.com/538/
For most of us the attacker is someone trying to make some money by scamming, stealing CC or installing a malicious app.