Firehose cannot deliver directly to a Redshift cluster in a private VPC without internet access or making the cluster public.

Using an Internet Gateway workaround compromises security.
1. Enabling an Internet Gateway exposes the Redshift cluster to inbound traffic from the internet, dramatically increasing the attack surface.
2. Many compliance frameworks and AWS Security Hub rules (e.g., foundational best practices) discourage making databases publicly accessible.

A best-practice alternative is to have Firehose deliver logs to S3, then use a Lambda or similar within the VPC to COPY into Redshift.

For real-time streaming, consider Redshift's native Streaming Ingestion which fits tightly into private network models.