They just released an attachments viewer for AGO Online. Hopefully it will come to Portal
I created an attachment viewer using Dashboard.
Also, you can install Collector for Desktop on your computer (get it from the Microsoft Store) and you can quickly view photos.
Are you talking about the attachments viewer template?
I need a template/app where I can view attachments, interact with a map, and edit a fields to collect notes. The closest thing I have found is the webapp builder, but it is missing the ability to view attachments.