Two-factor authentication is mandatory and cannot be disabled
Account Settings announces this when the member tries to disable 2FA while site policy forbids it (twoFactor.mandatory). UI shows Required on this site instead of Turn off.
Why this happens
Two-factor authentication mode is mandatory. Client-side gate before calling disable. API sibling: Two-factor authentication is mandatory on this site and cannot be disabled.
Diagnose and fix
1. Admin: switch mode to optional if members should be able to turn 2FA off.
2. Members: keep using the authenticator; lost device → staff Reset user 2FA / sessions.
3. Distinct from Could not disable 2FA (API failure when disable is allowed).