Open RDS Console - Subnet groups - Create DB subnet group.

Enter Name: <your-db-subnet-group-name>.
Enter Description: <your-db-subnet-group-description>.
Select VPC: your-vpc-id.
Select 2 Az that have 2 isolated subnet.
Seclect 2 isolated subnet: your-isolated-subnet-1-id and your-isolated-subnet-2-id.

Open RDS Console - Databases - Create database.

Select Engine type: PostgreSQL.
Select Full Configuration.

Pick Multi AZ 2 instance.

Select VPC and Subnetgroup id.

Select Vpc security group: <your-database-security-group-id>.

Select Engine version: 15.14.
Enter DB instance identifier: <your-db-instance-identifier>.
Enter Master username: postgres.

Click Manage in AWS Secret Manager

Select DB instance class: db.t4g.micro.

Select Storage type: gp3.
Enter Allocated storage: 20 GB.
Enable Storage autoscaling: Yes.
Enter Maximum storage threshold: 50 GB.

Enter Backup retention period: 7 days.
Enable CloudWatch logs export: postgresql.
Click Create.
Confirm status: Complete.

Click Create database.
Wait until DB instance status is available.

Copy Endpoint address: <your-rds-endpoint>.
Confirm Port: 5432.

<your-rds-secret-arn>.Complete and includes only the two isolated subnets.available.postgres 15.14, db.t4g.micro, true.gp3, 20 GB, autoscaling 50 GB.false, port is 5432.7 days and CloudWatch logs export includes postgresql.