RDS Console Issue: Unable to Select DB Instance Type or Storage Type for Any Database Engine

Although I cannot read the language in the screenshots, I assume what is happening based on the visible fields and your description. Since the problem is isolated to the ap-northeast-1region and works in Osaka and Sydney, this is not a browser, cache, or cookie issue.

As to my understanding

The AWS Management Console hides backend API errors. When the console tries to load available instance types and storage options for a specific region and the background request fails, it simply leaves the dropdown menus empty or grayed out instead of displaying the actual error.

To me, the two most likely causes for this region-specific behavior are:

• Missing VPC or DB Subnet Group: You might have deleted the default VPC in Tokyo, or there is no valid DB Subnet Group. RDS needs to know which network subnets to use in order to calculate which instance types are available.
• Capacity constraints: AWS might be temporarily out of db.t4g.micro (Free Tier) capacity in your specific Availability Zones in the Tokyo region.

How to find the exact error and solve it

To find the definitive solution, you need to bypass the graphical console and force the AWS API to return the hidden error message. You can easily do this using the AWS CLI or AWS CloudShell.

Run the following command to attempt the creation via CLI:

aws rds create-db-instance \
    --region ap-northeast-1 \
    --db-instance-identifier test-troubleshoot-db \
    --db-instance-class db.t4g.micro \
    --engine postgres \
    --master-username adminuser \
    --master-user-password TemporaryPassword123! \
    --allocated-storage 20

How to interpret the CLI output

The command will likely fail, but it will return a clear, specific error code. Here is how to solve the most common errors it will output:

• DBSubnetGroupNotFoundFault or InvalidVPCNetworkStateFault: You are missing a valid network setup in Tokyo. Go to the VPC Console in Tokyo, recreate the default VPC, and ensure you have a valid DB Subnet Group configured in RDS.
• InsufficientDBInstanceCapacity: AWS currently has no Free Tier (t4g.micro) hardware available in your assigned Tokyo Availability Zones. You will need to wait for capacity to free up or select a non-Free Tier instance type.
• UnauthorizedOperation: Your IAM user is missing specific permissions (such as ec2:DescribeSubnets) in the Tokyo region.

Hello.

Is your AWS account a recently created account?
In that case, there might be some kind of restriction in place.
If the issue is due to a UI problem or a restriction imposed by AWS, the only way to resolve it is to contact AWS support.
AWS re:Post is a community forum site, so we can offer advice, but we cannot directly verify the issue within your AWS account.
https://console.aws.amazon.com/support/

By the way, what happens if I create it using the AWS CLI?
Since you can run the AWS CLI in AWS CloudShell, please run the CLI there and share any error messages if you encounter any.
https://docs.aws.amazon.com/cloudshell/latest/userguide/welcome.html

Based on the symptoms you're describing, this appears to be a console-specific issue rather than a service limitation or account restriction. The fact that you're not receiving explicit permission errors, and that the dropdowns are displaying options but rendering them as disabled (grayed out), suggests a browser or console rendering problem rather than an underlying service or IAM issue.

Here are some troubleshooting steps to help resolve this:

Browser-Related Troubleshooting:

1. Clear your browser cache and cookies completely, then restart your browser
2. Try using a different browser (if you've tested Edge and Chrome, try Firefox or Safari)
3. Disable browser extensions temporarily, particularly ad blockers or security extensions that might interfere with console functionality
4. Try accessing the console in an incognito/private browsing window
5. Ensure your browser is fully updated to the latest version

Console-Related Steps:

1. Sign out of the AWS Management Console completely and sign back in
2. Try accessing the RDS console from a different network (such as a mobile hotspot) to rule out network-level issues
3. Check if JavaScript is enabled and functioning properly in your browser

Alternative Approach: If the console issue persists, you can create and modify RDS instances using the AWS Command Line Interface (CLI) as a workaround. The CLI bypasses the console entirely and interacts directly with the RDS API. You would use commands like create-db-instance with parameters such as --db-instance-class, --allocated-storage, and --storage-type to specify the configuration that's currently unavailable in the console.

If none of these steps resolve the issue, I recommend visiting the AWS Support Center (https://console.aws.amazon.com/support/) to report this console behavior, as it may require investigation by the console team to identify and resolve the underlying cause.
Sources
Creating an RDS for SQL Server Developer Edition DB instance - Amazon Relational Database Service