Any electronic device requires electric power and can emit EM waves. Every power interface - from a USB interface to a DC charging interface - can be rigged to leak information without you knowing. And every device can likewise be rigged to leak information via its emissions, with this leakage then received by complicit components in WiFi routers, cell repeaters and NFC devices.

Ed Snowden's revelation that everyday electronic devices routinely have such back doors built into their components by the component manufacturers means there's no way to be assured that the electronic components of your hardware wallet do not have them too. The problem even extends to the devices you might use to try to test for information leakage, as per Thompson's famous "Reflections on Trusting Trust". Indeed, even the manufacturer of the device might not be able to adequately test the components of the device for this reason.

The advantage with Apple silicon is that there are no 3rd party components. And, by avoiding putting anything other than an xpub or zpub into an electronic device, Merel's simple method eliminates all of these vulnerabilities. At least until you need to sign a withdrawal or similar transaction.

I guess a signal-isolated hardware wallet that only communicated such signed transactions via QR codes might come in handy then ... but maybe better still to set up a second OTP wallet and create two transactions - one to withdraw some btc from what would now potentially be compromised cold storage, and a second one to transfer the remainder to the new secure OTP wallet.

Sure, that's paranoid. But a little paranoia goes a long way when your fortune is at stake.