Frame challenge - 2FA doesn’t solve any problems that are actually problems for the homeless.

A homeless person has a vastly different cybersecurity paradigm, specifically, they don’t need much in the way of cybersecurity. Nobody is stealing a homeless person’s identity.

Given that, just let them disable it, and let them just use a password. It’s fine to rate limit them if they forget the password a few times, but let them keep trying to log in until they remember it.