@Duchemin, Dominique
Thank you for posting in Microsoft Q&A forum.
I think it's difficult for us to get such a report, you may first try to follow below article to find who initiated restart of SCCM client:
https://eskonr.com/2016/11/how-to-find-who-initiated-restart-of-sccm-configmgr-client/
(Third-party link, just for your reference)
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