IAM roles are a secure way to grant permissions to applications running on an Amazon EC2 instance to make calls to other AWS services. IAM roles are entities that have specific permissions policies attached to them. You can create an IAM role and associate it with an EC2 instance when you launch it or later. The applications on the instance can then use the temporary credentials provided by the role to access AWS resources that the role allows. This way, you do not have tostore any long-term credentials or access keys on the instance, which reduces the risk of compromise or misuse12.

The other options are not correct, because:

Security groups are virtual firewalls that control the inbound and outbound traffic for your EC2 instances. Security groups do not grant permissions to access other AWS services, but rather filter the network traffic based on rules that you define3.

AWS Firewall Manager is a service that helps you centrally configure and manage firewall rules across your accounts and resources. AWS Firewall Manager works with AWS WAF, AWS Shield Advanced, and Amazon VPC security groups. AWS Firewall Manager does not grant permissions to access other AWS services, but rather helps you enforce consistent security policies across your AWS infrastructure4.

IAM user SSH keys are credentials that allow you to connect to your EC2 instance using SSH. SSH keys do not grant permissions to access other AWS services, but rather authenticate your identity when you log in to your instance5.

Using an IAM role to grant permissions to applications running on Amazon EC2 instances - AWS Identity and Access Management

IAM roles for Amazon EC2 - Amazon Elastic Compute Cloud

Security groups for your VPC - Amazon Virtual Private Cloud

What is AWS Firewall Manager? - AWS Firewall Manager

Connecting to your Linux instance using SSH - Amazon Elastic Compute Cloud