I went to Admin Dashboard -> Libraries -> Scan All Libraries. I believe that does the “Scan for new and updated files” by default. According to this reddit thread, you only need to replace metadata if you’re utilizing the new features like chapters in audiobooks.
The Scan All Libraries should suffice for the basic set-up (followed by manually triggering the optimize database scheduled task). However, if you want it to catch some of the new features (really only chapter support for audiobooks springs to mind), that requires a “replace all meta-data” level scan.