The optimal solution for secure sharing and management of custom SQL UDFs across different teams in Databricks is embedding UDF definitions within Unity Catalog‘s shared metastores with fine-grained access control. This approach offers several benefits: 1. Unity Catalog‘s shared metastores provide a centralized platform for metadata management, including UDF definitions, enabling all teams to access and use UDFs without duplication or manual sharing. 2. Fine-grained access control allows organizations to set specific permissions, ensuring only authorized personnel can view, modify, or execute the UDFs, thereby enhancing security. 3. Centralized management facilitates easy updates and maintenance of UDFs, ensuring consistency and minimizing version control issues. 4. Ease of access is maintained, as team members can effortlessly discover and utilize UDFs, promoting collaboration and efficiency. Thus, leveraging Unity Catalog‘s shared metastores with fine-grained access control is the most effective strategy for secure and efficient UDF sharing and usage in Databricks.