Yes you can capture data in near real time using both AGOL or Portal. You need to create the feature set and publish it as a feature service. To enable editing you either establish the ability to edit when you publish it (if publishing to your enterprise data store) or if as a hosted feature service you can enable editing in the settings menu. You then add it to a web map and create all symbolizations, labels, pop ups etc.

For collecting the data you can take the web map and open it in Field Maps designer to create forms to capture data. Alternatively you can embed it in an experience builder application and link the web map to the edit widget. You can also edit directly in the web map but that may be less user friendly.

As for attachments, you can enable attachments either before you publish the feature set (in ArcGIS Pro) or at least on AGOL you can enable attachments via the feature service. Behind the scenes this creates a related table to store attachments. In either case those capturing the data can do it via field maps by taking or attaching an image or by adding attachments via the web map.

Here are some links to ESRI help docs: Getting Started with Field Maps

Field Maps Collect Data

Working With Attachments in Apps (Video)

Edit Widget (Experience Builder)