Getting started refers to unsupported versions of core

Tried to mark the pages as deprecated, but there is no option for that.

It is only possible to mark deprecated the single documentation pages. Documentation guides can only be marked as Needs maintainers or Seeking co-maintainer(s).

I have disabled the links for the 3 Drupal 9 guides/pages. And all the pages are now deprecated.

So, it look better but the out of date pages are still there.