Dear Faith,
Good day!!
Apologies for the inconvenience caused and please don’t worry, let’s work together on your concern and move towards a resolution path.
I understand your concern and to my knowledge, when you make the changes to the responses Excel workbook, there will be issues with the synced responses Excel workbook and the recommendation is not to make the changes to the synced responses Excel workbook. Moreover, I have also tested with protecting the synced Excel workbook where I encountered the similar behavior.
I agree with you having the ability to make the changes to the synced responses Excel workbook and keep connection with the Form will benefit the users and I suggest you to add your valuable idea as a feedback in the Microsoft Forms · Community which is the best place to share our ideas and improve the Microsoft Products.
Moreover, as a workaround, if the Form is created in the SharePoint Online site and synced responses Excel workbook in the shared Document library, where you want to prevent other users to view the responses Excel workbook, they are two alternative ways:
Alternative 1: Creating the Form in your OneDrive for Business where the responses Excel workbook will be stored in your OneDrive for Business, where other users won’t be able to access it unless you share the file.
Alternative 2: If you don’t want to the Form to be created in your OneDrive for Business, you can try removing the permissions on the responses Excel workbook:
Go to the responses Excel workbook> Right-click> Manage Access> Click on the three dots> Advanced Settings> Stop Inheriting permissions> Grant Access to yourself with the Owner permission> Remove the Site groups and other members having access to the group.
My recommendation is using Alternative 1 because you can share the Form link to responders for submitting and use the responses Excel workbook only to yourself.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia