This permission setting should be checked if the custom CRM object is not available in New Data Stream configuration. The user who connects the Salesforce CRM connector must have View All permission for the custom object in the source CRM org. References:https://help.salesforce.com/s/articleView?id=sf.
c360_a_data_cloud_salesforce_crm.htm&type=5

A Data Model Object (DMO) that inherits the name, shape, and semantics of the reference object is called a Standard DMO. A reference object is a predefined object in the Data Cloud data model that represents a common entity or concept, such as Individual, Order, or Product. A Standard DMO is a copy of a reference object that you can use to ingest data from a specific source without modifying the original reference object.
A Standard DMO has the same fields and relationships as the reference object, but you can add custom fields or relationships to it if needed. References: Data Model Objects

If no file name is specified in AWS S3 data stream during ingestion, the system does not fetch any file and the data stream shows an error. AWS S3 data stream is a feature thatallows you to stream data from Amazon Web Services Simple Storage Service (AWS S3) to Data Cloud in near real time. You need to specify the file name or prefix of the files that you want to ingest from your S3 bucket. If you leave this field blank, the system cannot find any matching files and returns an error message. References: AWS S3 Data Stream

A window function is a unique requirement of a Streaming Insight query. It defines the time interval for the query to run on the streaming data and thefrequency of the query execution. References:https://help.salesforce.
com/s/articleView?id=sf.c360_a_streaming_insights.htm&type=5

This configuration will ensure that Data Cloud only ingests new files from the Amazon S3 bucket and updates or inserts new records into the data stream without deleting existing records. References:https://help.
salesforce.com/s/articleView?id=sf.c360_a_data_cloud_amazon_s3.htm&type=5