You’re correct that user_support_manager is the right role, but it has a limitation: it can only remove MFA devices if the manager has the user’s MFA code or recovery codes. Only admins can disable MFA without those.
If you want to remove MFA without needing a code, you’d need to use the User API to clear the user’s MFA data. Also, confirm that both support managers have the same role assigned under their registrations in the FusionAuth application. Check this under each user’s Source tab in the Admin UI under registrations.roles.
More details: