DLT pipelines are still on runtime 16.4 which doesn't have support for st_point yet. See details here https://learn.microsoft.com/en-us/azure/databricks/release-notes/dlt/

You should be able to use st_point in normal SQL editor as long as the cluster you are using is DBR 17.1 or above, it is not currently supported on classic SQL warehouses either as it is still in public preview. https://docs.databricks.com/aws/en/sql/language-manual/functions/st_point

To check the version of runtime your pipeline is running on you can use the following code:

SELECT details:create_update:runtime_version:dbr_version FROM event_log_raw WHERE event_type = 'create_update