Bug: Incorrect output file format when specifying XLSX output without output file

[berntpopp]

Description:

When specifying xlsx as the output format but not providing an output file name, the script defaults to writing the Excel output to a TSV file. This causes confusion and improper file handling.

Steps to Reproduce:

1. Run the script with the -x or --xlsx flag without specifying an output file.
2. Observe that the output is written in TSV format instead of XLSX.

Expected Behavior:

The script should either prompt the user to specify an output file name when xlsx is selected or default to a meaningful Excel file name such as output.xlsx.