I drag links from Safari into Agenda to make a “read later” list, by dragging the icon in the URL bar and dropping it into an Agenda note:
This creates an attachment in Agenda, with the “thumbnail and title” setting.
I would prefer it if it came in as a Markdown link. Barring that, “inline” would be a preferable way to render link attachments by default. But I think a link makes a lot more sense than attachment.
Agenda 7.0 on macOS 10.14.6