Your EC2 instance is running, but you cannot connect to it using SSH. What steps would you take to troubleshoot the issue?

I am preparing for AWS and cloud engineering interviews and came across this troubleshooting scenario. Suppose an Amazon EC2 instance is in the Running state, but I am unable to connect to it via SSH.

I would like to understand the troubleshooting process, including:

How to verify that the EC2 instance is running and has a public IP or Elastic IP.
How to check the Security Group to ensure port 22 (SSH) is open for the correct IP address.
How to verify the Network ACL and route table settings in the VPC.
How to confirm that the correct SSH key pair and username are being used.
How to determine whether the SSH service is running on the instance.
Which AWS tools, such as EC2 Instance Connect or Systems Manager Session Manager, can help diagnose or regain access.
What are the most common causes of SSH connection failures, and how can they be resolved?