Why is /mnt/overlay/wcm/core/content/sites/properties.html missing? Where can I copy a pre-created one (like core/...) to easy my work with?

Question

I am learning AEM 6.5 using "Build and Apply AEM elements to master components and websites!" on Udemy.

On step 43, "Lab: Create Content Root For We.Train", the following error appears - and I assured I had no mistakes in following:

Not Found

Cannot serve request to /mnt/overlay/wcm/core/content/sites/properties.html

ApacheSling/2.7 (jetty/9.4.30.v20200611, Java HotSpot(TM) 64-Bit Server VM 1.8.0_202, Windows 10 10.0 amd64)

I have found this link which seems to be the solution, but I don't know how to apply it (I am very new): Show/hide properties of a page created using a template