It is extremely annoying how opening a document in a new window works in Circuit Studio.
One would think that you could drag/drop a document from the original window to the new window, but this is not the case
It appears that the only way to open a document in a new window is to right-click an already open document and select "Open in new window", or to dock the Projects panel in the window you want to open a document in, and double click on the document.
See video for illustration of what I mean: