PSA: if your financial institution/government/ is using SMS codes (aka PSTN MFA) for multi-factor authentication they are practically worthless against a determined attacker who can use SIM swap or an SS7 attack to obtain the code. Basically you are secured by a single factor, your password. If your password is compromised it may be sold via black hat marketplaces and purchased by an attacker who would then likely attempt to break that second factor.

The best way to protect yourself is to use a unique password; a password manager especially helps with this. Sometimes institutions will offer "Authenticator" (TOTP) as a second factor, or PassKey authentication, both secure alternatives to SMS codes.

Here in Aus I'm working with Electronic Frontiers Australia to try and force some change within government and financial institutions (via the financial regulator). Most banks here use SMS codes and occasionally offer a proprietary app. One of the well-known international banks, ING Bank, even uses a 4 pin code to login to their online banking portal. 😖

Unfortunately SMS codes are a legacy left from old technology and a lack of understanding or resourcing by organisations that implement it. Authenticator/TOTP tokens have been around for 16 years (and standardised for 13 years), and PassKeys are relatively newer. There is a learning curve but at the very least every organisation should at least provide either TOTP or PassKeys as an option for security-minded users.