App/Add-in and Extension
The Webtrends SharePoint Tag Installer is SharePoint Hosted Add-in that can be deployed to individual site collections via the app catalog and then enabled to add the tracking code to classic experience pages.
This Add-in is site scoped and will tag the site collection and all sub-sites.
For modern view support, the Webtrends SharePoint Online Modern View Extension can also be installed on each site collection and sub-site to ensure tracking of both experiences.
The Webtrends SharePoint Online Modern View Extension requires that the Webtrends SharePoint Tag Installer be installed and enabled on the same Site Collection to function.
SPFx extensions are web scoped, and must be installed on individual site collections and sub-sites.