Good days, thanks for posting in this forum.
Unfortunately, it is currently impossible to obtain the URL of the attachment in the List item through the API. As you said, it only returns a Boolean value. But you can try to use Power Shell to obtain relevant information about Attachments:
SharePoint Online: Get Attachments Report in a List using PowerShell
Non-official, just for reference.
Please do let us know if you have any further queries.
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