AWS Schema Conversion Tool Issue: Database Name doesn't appear under Schemas of the Source, in the left pane of the AWS SCT

It seems you're experiencing a misunderstanding about how AWS Schema Conversion Tool (AWS SCT) displays source and target databases in its interface.

In AWS SCT, the source and target databases are displayed in separate panels, not nested under each other. Based on the standard AWS SCT interface layout:

1. The left panel shows only your source database schema in a tree view format. This is where you'll see your MariaDB database schemas.

2. The right panel displays your target database schema (PostgreSQL in your case) in a separate tree view.

3. The middle panels show conversion details and action items.

Your target PostgreSQL database should not appear under the Schemas section of your source database in the left pane. Instead, it should be visible in the right panel of the AWS SCT interface.

To convert a schema from your source MariaDB database to your target PostgreSQL database:

1. Select the checkbox for the schema you want to convert in the left panel
2. Choose that schema (it will be highlighted in blue)
3. Right-click on it and select "Convert schema"
4. After conversion, you can view the converted schema in the center panels
5. When ready, you can apply the converted schema to your target database

The schemas are "lazy loaded," meaning AWS SCT retrieves and displays the current schema from your database when you select an item from the tree view.
Sources
Converting schemas using AWS SCT - AWS Schema Conversion Tool
Viewing the Project Window in AWS SCT - AWS Schema Conversion Tool