Complete analysis could not detect what preventive auto-protect could

Issue abstract:
Norton complete analysis could not detect what preventive auto-protect detected; how is it possible?
Detailed description:
My mother Intel MacBook Pro had a Finder organised upside-down and a keyboard problem of repeating letters on clics, so it was very clear that it was infected by a malware.
Norton complete analysis with all the settings at maximum, both about detection strength and included sections; it found nothing.
On last occurrence, I loaded her files for a transfert on M3 MacBook Air, and Norton preventive detection auto-protect deleted 9 exemplaries of " Le discours rapporté au passé-exercice.doc " for containing a Trojan of severity 2/3.
Product & version number:
Norton 365 for Mac; version 25.2.0.
OS details:
Mac OS Sequoia 15.3.
What is the error message you are seeing?
Threat detected in a file.
If you have any supporting screenshots, please add them:

Bonjour Oppenheimer,
La menace bloquée correspondait à la capture d’écran de l’historique que vous nous avez fournie. Avez-vous effectué une analyse complète du système avec votre produit Norton ? Avez-vous téléchargé Malwarebytes pour MAC et effectué une analyse complète ?

SA