When you are composing in Plain Text format, you’ll get prompted how you want to attach the file when selecting a file that is located on OneDrive or other Cloud based storage
Note: The above option is not available when using OneDrive for Business (SharePoint). In the section for Meet Your Personal Vault, click. If I edit a file on my Desktop, it edits them on a folder called 'Desktop' under another folder called 'OneDrive' - the folder that syncs everything to the cloud. On my windows laptop, the desktop is my OneDrive desktop.
