Sorry but I think I don’t understand.
I have not created or assigned any pages as a portfolio page. There is no portfolio page between the pages. However, the Portfolio page can be reached from a project link.

The page you see in the video is a page created by the visual composer that shows a summary of the projects, but this has a different name than “portfolio” and I have not assigned the portfolio template.

I just tried to create a page, assigned the portfolio template and saved. But it doesn’t change anything the projects always have / porfolio / in the slug.

You can make a video showing the steps. I followed your documentation, but this particular step is not specified.

Thank you