Cubase Pro has a control room, which isn’t there in LE. The signals route differently. I think there’s a video about the control room somewhere. Anyway, if you go to Devices > VST Connections, you’ll see this new tab called “Studio”. The Output tab in a typical setup shows Stereo Out as “Not Connected” 
The job has been moved to the studio tab, because you now have multiple outputs including cue mixes and alternative control room monitors. It’s been a while, but I think you want to hit Add Channel, then Add Monitor. After that, you make assignments to your audio interface. Now if you open the control room window, you have the controls for your monitors at the bottom: blue on/off switch, big red button to set the level, stereo/mono button, and so on.
if you don’t want to deal with the control room, you can turn it off in the Studio tab. I think it then works like what you’re used to, with stereo out being routed on the output tab.