Informatica Source Qualifier not working from Windows ODBC data source (system DSN) from Excel xlsx file
To use an Excel file as a source you need to define a named range containing the cells with data (that's Step 1 of the instruction you referenced in the question).

All the named ranges found in the file will be shown in the Select tables pane. After you select a table (i.e. a range) and click OK, a new source will be created.



You can also consider converting the Excel spreadsheet to the CSV format and using simple flat files as a source. If you're in a Windows environment and have have Excel installed, there's a VBS script that can help you automate this process.