OneDrive - How to save Office 365 documents online only?

Saving files to OneDrive will usually result in a copy in the \OneDrive folder on the HDD.
I am seeking a way to store Word/Excel documents within a OneDrive folder but only online, no copy on HDD.

Within (for example) Excel, with an open document, I would go for File > Save As...
Then there is a OneDrive option, which will, I assume, result in storing a local copy of the file, within \OneDrive, BUT there also seems to a be 2nd option requiring a login.

What is the difference between these two?
Is what I want (online storage of Office documents) possible?

Thanks.

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The following link doesn't really address your question but may give you another option to think about..
[Help] CMD command to free up space in OneDrive? : Windows10