Did you ever get a solution or answer on this error? Apparently partition overwrites are no longer a preview feature, they were released in version Databricks SQL version 2023.40 (see link below). My SQL warehouse is using 2023.40 but I am still getting the same "spark.sql.sources.partitionOverwriteMode is not available" error as you via dbt.

https://docs.databricks.com/en/sql/release-notes/index.html

• Block schema overwrite is available when using dynamic partition overwrites.