While Autodesk encourages users to upgrade to newer versions of Revit, they continue to provide access to legacy tools like the Revit 2018 Extensions for valid subscribers. By following this guide, you’ve saved hours of searching through dead links and outdated forum posts.
You tried to install Update 2 without the base extension. Fix: Install RevitExtensions2018_x64.exe before applying any .msp (Microsoft Patch) updates.