Just to clarify: Delta tables still store data in Parquet under the hood, but Delta adds a transaction log (_delta_log) that enables ACID operations like UPDATE, DELETE, and MERGE.
That log layer is what Unity Catalog expects for full SQL DML support — which explains why converting the tables to Delta resolved the issue.
Thanks for sharing the resolution! It will help others hitting the same blocker.
In case it's useful to someone, here are the commands:
Convert existing Parquet folder to Delta:
CONVERT TO DELTA parquet.`s3://your-bucket/path/to/parquet-data`
Convert existing external table to Delta:
CONVERT TO DELTA your_schema.your_parquet_table
Create a Delta table directly:
CREATE TABLE your_table
USING DELTA
LOCATION 's3://your-bucket/path'
Greetings!!!!!