Will the "Attachment Viewer" be available via opening a map then clicking on Share => Create a Web App => Create a New Web App => Configurable Apps dialog as shown in the screenshot below? If so, when...
Thanks for the post - I see Attachment Viewer when I go to create a Configurable App from a Web Map.
Would you be able to share your web map publicly or with Peter K_ess so I can take a look? Alternatively, I would be happy to get a case going with Esri Support so a dedicated analyst can take a closer look at what may be affecting the dialog panel.