How to convert xla add-in files to xlsx. Available xla to xlsx converters.
Everything points to the fact that you cannot convert .xla files to .xlsx on any other Excel for add-in for that matter. XLA format is used for add-ons, plugins used to enhance the functionality of Microsoft Excel. The only thing you could potentially do is to import the .xla file to Excel and based on the imported functionalities produce or edit .xlsx spreadsheet.
Direct conversion of xla file to xlsx is not possible. Different not compatible formats.
In a word, direct xla to xlsx conversion is not possible.
So don't expect any so-called xla to xlsx converter or xla to xlsx free online conversion tool available.