How to enable "Schema Validation" for Kinesis Firehose Stream?

We want to enable the schema validation for Firehose streams as described here: https://docs.aws.amazon.com/firehose/latest/dev/create-transform.html

Quote: "To enable schema validation, check the Enable schema validation checkbox and then choose either Apache Avro or JSON schema for the Data format for Kafka record value, and specify the AWS Glue schema registry region."

However if I create the Stream manually there is not such option. The only options are Source Settings, Delivery Stream Name, Transform and convert records - optional, Destination settings, Advanced Settings. There aren't any sub settings to configure the schema.

We looked into the boto3 documentation to find it in the API here: https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/firehose/client/create_delivery_stream.html

Again no word about schema validation. Does this feature even exist?

What are the steps to make this available and why is schema validation only possible if the source is a MSK Cluster? Ideally we want to use Direct PUT.