[4lun]

Slight mitigation to this is you can add an automation via the Shortcuts app to be triggered when airplane mode is enabled, and set the actions to immediately lock your device and disable airplane mode

Downside is that you need to manually disable the automation if you actually wish to use airplane mode (and also remember to re-enable it when done)

[NamTaf]

I've set two automations: 1) When airplane mode is activated, lock the screen. 2) When airplane mode is activated, turn it back off. That'll give me the most opportunity to either track it and/or lock it down remotely.

I can remember to disable the shortcut whenever I fly and need to enable it.

If they pop my SIM (my provider doesn't use eSIMs...) then there's a PIN on it to prevent use in another device.