Hi, I answer to myself.
Seems I found a solution with this post :
https://help.nextcloud.com/t/internal-server-error-after-upgrade-to-nextcloud-13/28127/6
I added the line :
'debug' => true,
So I can carry on the upgrade with the web interface.
But one warning occurs :
The following app has been deactivated : files_reader (not compatible)
Why that happen?
Is this a critical issue?
How to fix this files_reader bug?
Thanks,