Enable RSS for SharePoint 365 Online

SharePoint 365 Site --> Site Settings --> RSS

 

 Configure RSS for whole site

 

Still we can't have RSS  under "Library settings"

 

Document Library settings --> RSS settings

 

Configure RSS feed settings for "Library"

 

Now we can see RSS under Document Library 

 

Open Outlook --> RSS Feed

 

Enter Document Library URL, Outlook will auto integrate with RSS xml

 

 It is done, We can see related Docs