An APPXUPLOAD file is a single package file that contains multiple app packages or app bundle for uploading to Microsoft Store. It is generated automatically by Microsoft Visual Studio when developers package their app for publishing to the Microsoft Store. In addition to an APPX file, the APPXUPLOAD file contains a symbol file that analyzes app performance after it is published to the Microsoft Store.
AAPXUPLOAD File Format - More Information
The APPXBUNDLE files are saved to disc in binary file format, with their file format specifications not available publicly.