The SQL Server Developer edition includes all the functionality of Enterprise edition, but is licensed for use as a development and test system, not as a production server. SQL Server Developer is an ideal choice for people who build and test applications.
Quoting from SQL Server 2019 Licensing Guide:
Note: A production environment is defined as an environment that is accessed by end-users of an application (such as an internet website) and that is used for more than gathering feedback or acceptance testing of that application. Other scenarios that constitute production environments include:
• Environments that connect to a production database
• Environments that support disaster-recovery or backup for a production environment
• Environments that are used for production at least some of the time, such as a server that is rotated into production during peak periods of activity
It is rare that someone whose primary role is designing, developing, or testing software would also qualify as an “end user” of the software.