Which combination of steps should a solutions architect take to accomplish this?

Explanations:

Configuring a VPC gateway endpoint for Amazon S3 allows EC2 instances within the VPC to access S3 directly without traversing the public internet, enhancing security and reducing data transfer costs.

Making the objects in the S3 bucket public would expose sensitive user information, which is not secure and goes against best practices for handling sensitive data.

Creating a bucket policy that restricts access to the application tier running in the VPC ensures that only the intended resources can access the sensitive information, enhancing security.

Creating an IAM user with an S3 access policy and copying IAM credentials to the EC2 instance is not a secure practice; it risks exposing sensitive credentials and does not utilize the more secure IAM roles.

Using a NAT instance would allow EC2 instances to access S3, but it adds unnecessary complexity and potential security risks compared to using a VPC endpoint. A VPC endpoint is a better solution for secure access.