"If you want to transfer $1000 to account 1243567890, confirm with code ABCDEF".

Assuming an attentive user, this protects against malware silently changing amount and recipient on a transaction the user is making - an attack the banks were struggling with. It also makes phishing much harder, since the attacker needs to convince the user to enter the code after reading this message.

Code-based 2FA is vulnerable to phishing where the attacker relays the phished credentials in real time. German banks were doing 2FA long ago, in the form of sheets of paper with one-time passwords (called TAN). Attackers were phishing those, so banks switched to "indexed" (iTAN) OTPs: The bank tells you which OTP to use, so someone who has just phished 1 or 2 won't be able to use theirs. Phishers started relaying the stolen credentials to the bank in real time, looking which iTAN the bank asks for, then asking the victim for the same.

Given these known capabilities of attackers, any 2FA method that is not phishing resistant and not bound to a specific transaction is not usable, and probably not better than SMS. Anyone can make a phishing site, running attacks on phone networks is harder.

Edit: Just realized that U2F would not be a suitable solution for banks, since it does not authenticate specific transactions, so malware could still swap recipient and amount.