Can't create any sort of RDS database

Based on the information provided, your inability to create an RDS database instance is likely due to insufficient permissions. Even though you mentioned being an authorized user with "full permissions," there are several common permission-related issues that could prevent you from creating RDS instances:

1. Missing specific RDS permissions: You might be missing the rds:CreateDBInstance permission, which is essential for creating database instances. This is a common issue even when users believe they have full access.

2. Missing related permissions: Creating an RDS instance requires permissions for multiple AWS services, not just RDS. For example, you might need permissions for creating DB subnet groups (rds:CreateDBSubnetGroup).

3. Service Control Policies (SCPs): If your AWS account is part of an AWS Organization, there might be SCPs applied at the organization level that restrict RDS creation regardless of your user permissions.

4. IAM role configuration: The IAM role you're using might have the correct policy attached (like AmazonRDSFullAccess), but there could be other policies or conditions limiting your access.

To resolve this issue:

• Ask the account administrator to verify that you have the necessary permissions, specifically rds:CreateDBInstance and related actions
• Check if there are any SCPs in place that might be restricting your actions
• Ensure that you have permissions for any related services needed for RDS creation (like EC2 for networking components)
• Verify that you're operating in the correct AWS region where you have the intended permissions

If the issue persists after confirming these permissions, it could be a technical problem with the AWS console, and you might want to try using the AWS CLI or SDK as an alternative method to create the database.
Sources
CloudQuest - Database in practice step - permissions issue | AWS re:Post
RDS instance issue | AWS re:Post
Known issues for Amazon RDS Custom for Oracle - Amazon Relational Database Service

Hello.

Generally, if the IAM user you are using for an operation does not have enough permissions, an error message will be displayed when you press the Create button.
In your case, no error message is displayed and the spin mark appears forever, so there may be another problem.
Please open the developer mode of your browser and check for network issues.
If you are experiencing network issues, try connecting from a different browser, PC, or network.
Also, just to be sure, check the CloudTrail event history for the RDS creation event to see if a permission error occurred.
https://docs.aws.amazon.com/awscloudtrail/latest/userguide/tutorial-event-history.html