Recently I’m using the TOTP feature a lot, also as a result of the new reports like ‘Inactive 2FA Report’ 
All the sites I activated gave me 1 or more backup codes for recovery mode. I like to store them in a structured solution (multiple records of text fields). Unfortunately this is not possible right now. Therefore I use the Notes field now as an unstructured solution. The additional fields is not a handy workaround, because the value of a field is single line, and sometimes you get 6 backup codes