We slowly need to interface with an app at work that uses fixed-width too. It does not sound that bad if you hear it but it sucks to figure out where you are missing whitespace when most fields are not used and therefore all whitespace. Oh, and of course there are a lot of fields, also are aligned/formatted differently based on their type and has thin/no/wrong documentation. And I have yet to find a simple but decent “debugger”.
My EU bank never ever used my phone number to verify anything. They only used it to contact me on some occasions. 2FA is done through their app.