Hello, Fabien MIETURKA
Welcome to Microsoft Community.
I realize that you have encountered a problem that the result of the Forms quiz won't automatically update in Excel, and I understand how you feel.
We've tried to replicate the issue here.

I would like to explain to you that the synchronization of results takes some time. What you might be experiencing is a synchronization delay issue.
- When we directly click on Excel file (red box 1 in the above picture), it does not update immediately. but after waiting for a few minutes, the results will be automatically updated in Excel files.
- When we click on "Download a copy" (red box 2 in the above picture), because this should generate a new file based on the current Forms results, you can immediately see the updated results.
So, please wait for a while and see if the Excel files is updated.
If the results still do not update after waiting, please click "Disconnect and sync to a new ...“. (bule box in the above picture).
It will generate a new Excel file. When you click on Excel file (red box 1 in the figure) again, you can see the Excel file with the latest results.
Additionally, I sincerely suggest you send your feedback in Forms to let the Forms team know the inconvenience cuased by the delay of result sync.

Thanks for your understanding and cooperation.
Best wishes,
Lucia Wu - MSFT | Microsoft Community Support Specialist https://learn-attachment.microsoft.com/api/attachments/c3f7387c-17a3-4e04-903a-150b4e2bf8c6?platform=QnA