A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
It could be something missing when the excel is exported by code. The file size is difference between the two files. Try acSpreadsheetTypeExcel12Xml
You can try repair the excel file by File > open > Open and Repair
Reference:
Fixed: Excel Cannot Open the File Because of File Format (wondershare.com)
You can also raise a ticket to Microsoft.
Please contact your admin/IT department create a support ticket via Microsoft 365 Admin Center> Support> New service request. That support team there will have the correct channel and resources to help you investigate more and find what exactly the reason has caused this situation.
Best Regards,
Snow Lu