The library customers can install app called "Google Authenticator" provided they own a smartphone. It works without network connectivity.
Just use the app to scan QR code when creating a Gmail account. Or do it anytime later. Then never use network connectivity to generate the 6-digit 2FA code.
Just use the app to scan QR code when creating a Gmail account. Or do it anytime later. Then never use network connectivity to generate the 6-digit 2FA code.