Hi  @stemill ,

The way of connecting to Iceberg tables managed by Glue catalog that you described is not officially supported. Because spark_catalog is not a generic catalog slot – it’s a special, tightly‑wired session catalog with a lot of assumptions baked into the runtime. Overriding it with an Iceberg SparkCatalog breaks those assumptions.

It's important to define which catalog is the central data catalog: Glue or Unity Catalog?

If it's Glue, then you should check what is the official way of writing to a Glue-managed Iceberg tables from an external writer (Databricks). It usually goes through an Iceberg REST API.

If it's Unity Catalog, then you should convert Glue tables to Unity Catalog managed tables (the data can stay in the same S3 bucket). Then, they can be accessed from external readers/writers via the  Unity Catalog Iceberg REST API.  

Hope it helps.

Best regards,