Hi @Jeremie GLAIS ,
I apologize for misunderstanding your question.
Thank you for your time and explaining it to me in detail.
The settings in the previous answer are for external users, you're reporting an error because you can't remove permissions for internal users. Please check if you have Full control permissions for this file/folder/library. This is by design, only users with Full control can change the delete permission.
When I grant full control permissions, the "access is not available because you are not the owner of this item" error does not appear.
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