Lots of hate for SMS as 2FA here. By no means perfect but does anyone know of a viable alternative? Genuinely curious as this is a problem we have hit deploying

Lots of hate for SMS as 2FA here. By no means perfect but does anyone know of a viable alternative? Genuinely curious as this is a problem we have hit deploying financial services applications for predominantly underbanked / non tech savvy users. So, an authentication method that: - Is without dedicated hardware, as hardware is expensive, difficult to distribute and if it's a USB there is no guarantee that a user has a laptop. - That functions on feature phones (yes, they are still out there), or at the least phones without biometrics, as most don't. - That doesn't require the user to do anything extremely complex, as ironically this is the part where a lot of fraud occurs. Eg During a mobile banking rollout, customers were asked to register their phone number at an ATM. However many customers of the bank weren't familiar with ATMs (they banked at branches) and the people they requested help from linked their own phones and stole their cash.