Yes you can. In order to stream your desktop you will need to set a virtual camera software.
Some recommended tools are:
- ManyCam: https://manycam.com/ (Windows + Mac)
- SparkoCam: https://sparkosoft.com/sparkocam (Windows)
- CamTwist: http://camtwiststudio.com/ (Mac)
- Ecamm Live: https://www.ecamm.com/mac/ecammlive/ (Mac)
- NDI: https://www.newtek.com/ndi/tools/ (Windows)
As for NDI Tool, you will need both NDI Scan Converter and Virtual Input.
After setting up a virtual camera, you can simply select it in Loola as a video source: