Blender: Troubleshooting intransparent background with Freestyle and Eevee

Recently, I used Blender 2.83 to create a background image with many barrels which I did not want to draw by hand. David Revoy wrote a comprehensive tutorial about how to achieve that here: https://www.davidrevoy.com/article305/tons-of-potions-part-1-3d. However, newer versions of Blender seem to render edges using the Freestyle rendering method. You can find a quick introduction …