Security Defaults provides preconfigured security settings such as MFA – Multi-factor authentication for all users, blocking legacy authentication protocols, etc.
Any tenant created on or after 22nd October 2019, will have this setting enabled for default.
An organization with complex security requirements could disable the security defaults and consider using Conditional Access instead.
To disable Security default, login to Azure Portal
Navigate to Azure Active Directory > Properties
Toggle it to No and Save.
Hope it helps..