@GianlucaMiele1- thanks for the response. This turned out to be a long reply but I hope there's something useful for you.
Arcade was my target to give a rich output in the popup dialog, without having to add in superfluous attributes into a feature class. I need to display an image inline whose location is derived from another field; I would also like to style some custom HTML by colour according to other attribute values.
This would then be pulled through into a basic Experience Builder project, but also available to the generic viewer for users preferring that. It is also my preference to keep things simple, much as the Experience Builder can sometimes be shoehorned into a working example - it's not IMO elegant or compatible enough just yet, and I find designing to a fixed screen size a hard sell when we've been responsive throughout our time with Web App Builder.
I would state however that the need for this is as another workaround - actually I've tried many ways of doing this using the product stack and none have yet been acceptable.
At the most basic level of requirement, I have a 3D dataset and want to view an associated image (or images) for a given feature. It needs to be automated, so no manual configuration of StoryMap or Hub or whatever. Can script where necessary, don't want to build and maintain a custom web app.
The "Attachment viewer" template doesn't work with 3D scenes, which would be the quickest and easiest win. If that suppoted Scenes, it would cover 80% of our requirement, and if I could use Arcade in the popup that would be 100% - job done.
I have also investigated the scripting capabilities (via the Python API) of StoryMap and Hub to achieve this, but wasn't able to get a satisfactory output. I had hoped to create a Hub site with pages for each feature in a feature class, a little auto-generated text, and a Scene centered on the feature - but the update_layout method is essentially undocumented, and the pages created programmatically have a habit of disappearing! See below...
Many thanks.