To increase security for our customers, as of February 1, 2022, Salesforce requires all users to use multi-factor authentication (MFA) to access B2C Commerce products, including Account Manager. When logging into Commerce Cloud Account Manager, users who don't use MFA receive a warning message stating that they aren't using MFA.
How: To learn more about Salesforce B2C Commerce MFA requirements, see Get Ready for Future Multi-factor Authentication.