Air gapped wallets can utilize QR codes to sign transactions. Look into PSBTs (partially signed bitcoin transactions). Gist is you can create a transaction fro

Air gapped wallets can utilize QR codes to sign transactions. Look into PSBTs (partially signed bitcoin transactions). Gist is you can create a transaction from any device that doesn’t have your private key … send that transaction via a QR code to your cold wallet, then your cold wallet can sign transaction and create a new QR code for the other device to use.