As you can see from the recent activity, the main Prefect repository is very active with ongoing development, including recent updates to documentation, design components, and core functionality. The last merged pull request was just a few days ago.
If you're starting a new project with Prefect, you should definitely use Prefect 3.x from the main repository at
https://github.com/PrefectHQ/prefect. Don't let any archived repositories concern you - they're just part of proper maintenance as the project has evolved.