Hi @Harry N Nomikos ,
According to my research, it is not possible out-of-the-box to drag and drop a attachment to the list.
- If you are using classic experience, you could try to use REST API to achieve.
- If you are using modern experience, you may try to develop SPFx.
Here is a demo of using SPFx web part to upload files as an item attachments:
https://github.com/SharePoint/sp-dev-fx-webparts/tree/master/samples/react-file-upload
Thanks,
Echo Du
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