Apply Information Rights Management to document library with edit permission to site admin or Member Group in O365.
so that one or few limited users can update or edit documents in IRM applied document library
Based on your description, my understanding is that you want to apply Information Rights Management to a document library.
Here is a link about how to set up Information Rights Management (IRM) in SharePoint admin center, you can use as a reference:
Here is a link about how to apply Information Rights Management to a library, you can use as a reference:
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