Is extending Bartik a recommended move? I'm starting a new Drupal 8 project. As first steps I need to choose a theme. So far, I have only experience with Bario, chosen initially for using Bootstrap 4. I'm now looking for a theme that's not using Bootstrap.

I'm considering extending Bartik. Is this correct, or should I extend a different theme?
Please have a look at the Drupal core themes no longer extend Classy change record.


  Bartik, Claro, Seven, and Umami are part of the product rather than
  the API and therefore it is not officially supported to extend them.
  These themes can change as part of a minor release and cause
  regressions to any themes extending them.


Means: No it's not recommended to extend Bartik. Extend Classy or Stable instead.