Why isn't the Attachments field showing up as a sub-object in a detail layout?

You also need to map the field to a field template. This is an "/attachmentTemplate" global template shipped with the base product.

Here are high-level steps in Oracle Visual Builder Studio:

1. Create the mapping on the overall Edit Layouts Rule Set area and not in a specific layout. This way, the mapping applies to all the Edit layouts that you have.
2. Click + Default Field Template to apply the mapping to all layouts, and then enter /attachmentTemplate in the template value.

   Because /attachmentTemplate is defined in the base Sales app, it doesn't show up as a value you can select. But you can enter this value. The leading slash tells it to get it from the base app.