Explanation
Two-factor authentication requires users to verify their identity with two pieces of information when they log in to Salesforce. One piece is their username and password, and the other is a verification code from an authenticator app or email or SMS.
References: https://help.salesforce.com/s/articleView?id=sf.identity_2fa_overview.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.identity_2fa_login_flow.htm&type=5