Announcing Shield: an Official Authentication library

I wonder if this means Myth/Auth will be abandoned at some point in the future.

There is no plans to abandon it in the future. 

And you can find a project Notice about it:

As of June 2022 CodeIgniter now has an official Authentication library, CodeIgniter Shield. If you are looking for an authentication solution for a new project then that is the recommended solution. If you interact with the project repository there may be delays in receiving response. Please direct support questions to GitHub Discussions or to CodeIgniter's Forums or Slack Channel.