What is a Right Drag and Drop?
A right drag and drop is a drag and drop interaction performed using the right mouse button (secondary mouse button) instead of the left mouse button (primary mouse button). A right drag and drop may have a different result than a left drag and drop when performed.
Most applications do not support a right drag and drop, which makes sense: users may expect that things can be dragged and dropped with the left mouse button, and maybe the action performed by the drop modified by holding a modifier key, but they probably won't expect that something that can be dragged with the left mouse button can also be dragged with the right mouse button with a different effect. This makes a right drag and drop effectively non-discoverable.
Personally, the fact that this is even an interaction that exists is news to me. I discovered it by accident on Windows 11's File Explorer. I assume that's the only way to discover it because I would have never intentionally tried to right drag something when as far as I know you only ever drag things with the left mouse button. I tried dragging tabs on Chrome with the right mouse button, but as I expected it didn't do anything. I'm not aware of any other applications at this time that support a right drag and drop, so I can't even conclusively state what convention they follow. I assume the idea that a right drag and drop displays a context menu-like popup menu feels the most intuitive, but without additional examples it's hard to say.
On a technical level, right drag and drop would be unlikely to be supported on webpages and web applications, since a right click will open the web browser's context menu, and the web developers will want to avoid overriding that. I'm not sure if it's possible to discern a left drag and drop from a right drag and drop on common cross-platform UI toolkits at this time (e.g. GTK, Qt). I assume there is a way, but there could be toolkits that simply don't make it easy to implement this behavior. Nevertheless, this interaction looks so unusual yet so intuitive that I almost want to create an application just to implement a right drag and drop.