This is a quick update to Sidecar (2.1) that re-enables dragging so you can get it moved over to a second monitor. Unfortunately I can’t set a default point on a secondary monitor, so you’ll most likely have to reposition it on every launch. It’s a start, though. I’ll work to come up with a solution for that.
You might be able to go into the HTML file inside the package and change the starting pixel position to reflect the actual location on the screen where you want it to appear, making the second parameter the positive or negative width (depending on the location of your second monitor) of your primary screen.
Source code is still up on Github.