Some search results mention outlook16.0.dll – that is usually a language resource DLL or a helper DLL, not the primary object library. Again, it comes with Office, not as a separate file.
In VBA Editor, after adding the reference, open the Object Browser (F2). Search for “Application”. The status bar or the library name will show “Outlook” and version 16.0. microsoft outlook 16.0 object library dll download
Since the library is part of Office, you already have it if you have Microsoft Outlook installed. You just need to ensure it is correctly registered. Some search results mention outlook16