Multi-factor authentication (MFA) is turned on by default for direct logins to production orgs as of April 8, 2024. Starting in Summer ’24, admins get in-app reminders if they don’t comply with the MFA requirement.
Where: The change to turn on MFA by default applies to Lightning Experience, Salesforce Classic, and all versions of the mobile app in all editions. The change to add in-app reminders applies to Lightning Experience and all versions of the mobile app in all editions.
How: For more information on these changes, see MFA Is On by Default for Direct Logins to Production Orgs and Salesforce Admins Get In-App Reminders If MFA Is Turned Off