Hi Alice,
I think you have asked this question before. Double-clicking is not implemented in the UI of RC.
It seems like you have changed the viewports, because by default the top left window has a blue marker. This is the viewport that the image that you select with the left mouse button will be displayed. The marker is missing in your screenshot. You can either restore to factory settings or manually attribute it to the viewport. How to do that is covered in the help - I don’t remember now. Maybe ctrl+1 and clicking the window or something…