I use iCloud Keychain, and 2FA wherever I can. For this I've mostly used OTP Auth.app: OTP Auth by Roland Moers
https://appsto.re/th/i4ovN.i but I'm also interested in the Hurricane Electric 2FA tool in their network app: HE.NET Network Tools by Hurricane Electric, LLC
https://appsto.re/th/UQ7jZ.i as it uses the iCloud Keychain for sync, rather than their own storage format.