...
There are also instructions included in your new custom app in the ./readme.html document.
Azure storage static sites
These applications can be hosted in Azure Storage Accounts using the static site feature.
Update env.js to supply an apiUrl, as a local relative path is assumed
apiUrl = "https://js.arcgis.com/3.29",
Create a static site by following this documentation:
Use Microsoft Azure Storage Explorer to copy your app
From …\WebAppBuilderForArcGIS\server\apps
To $web
Follow the remaining steps to
Add the app as content and register the web app