It started when I was exporting to the PDF and I was able to use a different export option. Processes nwjs, nwjs Helper, nwjs Helper (GPU) and nwjs Helper (Renderer) should all disappear from the Activity Monitor and the tray icon and dock icons should disappear.
Choose your version (if you have Mojave or Catalina, choose Mac OS X (64 bit).
This is your file for installation in VirtualBox.