Bitwarden offers this as well, but I don't really understand why you would want it. If someone compromises your password manager, 2FA is now worthless. Or am I misunderstanding how it works?
Your understanding is correct. 1Password requires a key in addition to the master password. And finally, 1Password can have 2FA for itself, which is stored on my Authy. These are reasons why I am comfortable storing my 2FA codes on it.
Bitwarden has 2FA support too, but does not have the unique key feature that 1Password has.
Bitwarden has 2FA support too, but does not have the unique key feature that 1Password has.