I am not anticipating a fix on this - it was an intentional decision by Microsoft.
To continue to use your Excel workbook that was synced to the Form, you can:
- Go to the Form and go through the process of syncing responses to a new workbook (breaks sync to original workbook)
- Create a Power Automate Flow to update the original Excel workbook
In this scenario, the old workbook with historical responses remains the workbook you actively use and is updated when the Form is submitted via Power Automate while the new workbook that is now synced to the Form is essentially a dummy - you can sync it by opening it if you want to see raw responses.
Alternatively, use your existing spreadsheet as a template for SharePoint/MS Lists - you should be able to upload historical data with the template as well. You can then use Power Automate to update the SharePoint List.
Hope this helps.