I made an app from a web map that has a Custom attribute display for the popup. In the popup are links to 2 different URLS. These work in the web app, but after making an app with AppStudio, the links are not there, but just the attributes in the table.
Currently custom popups are not supported, but they are something we intend to add in future. Likely will come with the new web map support in the next major release for Runtime.