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.
Multiple vaults too is nice but I know others have ways to limit exposure of passwords in similar manners.