In Community Builder, "New" button should not be visible in Case list. In spite of removing "New" button option for List views, the "Recently Viewed" list shows the button. However, all list views in Standard Sf page and all other list views in Community have no New Button for Case. Am I missing any other setting?
I contacted SF support about this exact issue - this "recently viewed" list view and the corresponding "new" button are part of the Napili template and cannot currently be removed/configured/disabled.
My best suggestion is to just make sure you configure the case creation template so that should one of your users use the "New" button at least the case creation layout is configured or limited to the fields that you want displayed.