Apologies I'm not going to answer your question but ask you one.
I'm trying to get to use prompt/quick actions and am having some difficulty in the workflow getting it to work.
Is there any chance you can show me how to get it working?
The Prompt() action cannot action against attachments. In that sense, you are really inserting a child object, which isn't in the scope of that function.
Thank you for your time.
Do you know a solution to dynamically ask user for an attachment?
Can you give me more details?
You can find everything in the Admin Help.