My Mac Outlook 2016 (aka Version 15) has been running real slow so I wanted to rebuild its database to clean up any nagging issues. Holding down the Option key while starting up Outlook 2016 does nothing. There’s a reason for that – there is no database to rebuild anymore.
According to this Microsoft Office for Mac blog post, the database has been replaced with SQLite that runs its own maintenance as needed. When fixes are needed, SQLite takes care of them silently says the post.