How to know who deleted few column in sharepoint list ?

Hey Bd2023-b​
I tried to use site audit without success but maybe it will work for you : 
https://support.microsoft.com/en-us/office/configure-audit-data-for-a-site-collection-a9920c97-38c0-44f2-8bcb-4cf1e2ae22d2#bkmk-activate-reporting

But you can try with purview audit if you have the required licences
https://learn.microsoft.com/en-us/purview/audit-log-activities#sharepoint-list-activities

To prevent people from modifying lists structure, you can either modify "members" authorizations, or create a specific SharePoint Role.

Change their permissions from "Edit" to "Contribute"

Hope it helps !
Best regards,
Bruce