Check if the file you are uploading contains any hidden files or folders.
To do this:

1. Open Windows File Explorer.
2. Navigate to the file or folder.
3. Click the View tab.
4. Check the box next to Hidden items.
5. Check if any additional files appear.
6. Make sure you’re including all the files you wish to upload.

If there are hidden files of folders, you should include them when uploading as they can also be contributing to the file size difference.