Have you tried dragging an attachment straight from your outlook email into a SharePoint library?
Did it work for you?
This doesn’t work in Chrome, but it does work in the Edge browser. Simply find an email with an attachment and open the modern library in Edge. Then drag the attachment directly into SharePoint Online.
I also tested if I could drag ‘n drop the whole email, but unfortunately that doesn’t work yet. Hopefully that will happen one day too.