How to Air-Gap Coldcard, Trezor, Ledger, and most other HW wallets

I know there are a lot of people moving HW wallets lately and are intrigued by the Coldcard air-gap features, which are definitely best of class. But for those with other hardware wallets, you can still get an air-gapped config with a Ledger or Trezor.

1. Install Electrum on an online machine (system-a)
2. Install Electrum on a PiZero.0 (air gapped) machine (system-b)
3. Craft your transaction on system-a, and start a PSBT saved to USB
4. Plug the HW wallet in to system-b and complete the PBST on system-b
5. Take the completed TXN file from system-b and broadcast it in system-a

DEFINATELY not as clean as Coldcard's method that does all this for you on-device, but it's still air-gapped. So long as you define air-gapped as not-networked. If you use a newer definition of air-gapped, then this might not fit.

Now all we need is for someone to start another run of PiZero.0 since all suppliers seem to only have the non-air-gapped version (PiZero.W)