If you specifically need the 2012 version for legacy compatibility or testing, here are the remaining ways to obtain it:

SQL Server 2012 End of Support: What are your options? - DSP Blog

Because of its legacy status, finding an official, direct download link from Microsoft for the full Developer Edition is difficult. Most official links now point to Service Packs or the Express Edition . How to Access SQL Server 2012 Developer Edition

| Version | Key Newer Features | | :--- | :--- | | | Azure Synapse Link, Parameter Sensitive Plan Optimization, Intelligent Query Processing | | SQL Server 2019 Developer | Big Data Clusters, Accelerated Database Recovery, UTF-8 Support | | SQL Server 2017 Developer | Graph Data Processing, Automatic Tuning, Python Machine Learning Services |