Hello and thanks @pauloamgomes
I did the changes to config.yaml I created .env.local with the content of .env.production and changed COCKPIT_HOST and WEBSITE_SITE_ROOT and same errors.
Probably the problem is the extra layers of virtualization (Docker, Docker-Compose) inside of a Virtualbox machine, nested virtualization never worked for me.
But I saw that the installation of Docker, Docker-Compose and Cockpit React Static Demo loaded my test server with extra 2GBs of files and applications just for a few web pages. I can not afford 2GBs of overhead for a website that can be installed among 5 or 30MB including a PHP Flat File CMS. I loved what I saw in your video, I tried hard, even I installed a secondary VM with Fedora 29 and reinstalled everything, and even worst, it gave me more errors. With all my regret I have to give up Cockpit, because it does not have a viable front-end out of the box yet.
I understand that for demo purposes efficiency can be sacrificed, but not in production. I would suggest you to cut complexity and overhead to a minimum, because installing a couple of GBs per shared account on a web server to manage a few pages is not viable, at least for me.
If you create a simpler straightforward and direct installation process, without extra layers of complexities and load, that takes the minimum resources of a RedHat/Centos or Debian server, that are the majority of web servers many of which are VPSs, I can foresee a bright future for your Cockpit React Static project.
Thanks and best regards