This project is not intended to be run locally with a dev server. As the focus on is on content and letting the theme take care of all the appearance and templating concerns.
But, if you do want to run this locally, such as for faster debugging and experimenting, I recommend following instructions and setup steps on this project:
It covers installing Ruby, Bundle and project gems locally (including Jekyll). It has a
Gemfile which you can use to get started. Though, that uses the standard GH Pages and Jekyll 3.9 approach. And also without GH Actions.