Putting the source somewhere else: easy, git push and change the URL in your doc.
Moving all the issues: hopefully someone must have done a script to fetch the issue and convert them.
Moving your CI: just rewrite your GitHub action away from these horrible yaml command. This is just going to be a bit more expensive than the 100% free GitHub plan.
Getting the community of millions of user that can report issues, propose PR and star your repository. Good luck with that.
The network effect of the community is the barrier to the change. Unless you do proprietary software, then you don't care.
