Hi @Matt
Are you trying to add attachments from OneDrive to Outlook with this problem?
There is currently no option to turn off the drag-and-drop feature in Outlook. According to my tests, you can add attachments directly by copy-pasting. However, the position of the attachment cannot be changed to the body of the message.
To get this feature more quickly, I have created a post in feedback collection website, and you could vote for it. Many features of our current products are designed and upgraded based on customers’ feedback. You can also make suggestions on that website and hope Microsoft will notice this in the future. Thank you for your understanding and support.
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