Embedding doesn't work with imported project from Github

🐛 bug report

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project
  adheres to.
• I have searched the issue tracker for an issue that matches the one I want
  to file, without success.

Description of the problem

I'm not sure if I'm missing something but I searched in questions and passed issues and couldn't find the answer. It seems for project imported from github, there no option to an embedded url. The github repo is public and seems that option shows if you create a new sandbox from scratch but not if you create the sandbox by importing from github. I noticed an option to change the repo to public which made the sandbox a readonly, but even then the option for an embedded url didn't show

How has this issue affected you? What are you trying to accomplish?

I writing an article and would like to share a demo of the code.

To Reproduce

create a new project by importing from a github repo and try to retrieve the embed url option.

Link to sandbox: link (optional)

Your Environment

Reproduce the missing embed URL option by importing the linked public GitHub project into CodeSandbox, using the sandbox link and its /src/pages/index.tsx entry as the example. Trace the imported-project flow and compare it with creating a new sandbox from scratch; done means an embed URL option is available for the imported project without making it read-only.