Checkout button is not displayed on the latest version of an article. Removing the conditions on the Checkout UI Action results in an error message that the article is already checked out.

Steps to Reproduce:
1. Open article and observe there is no checkout button.
2. Remove the conditions from the ui action and click the button on the KB article: message says it's already checked out.
3. Check related list: No new versions have been created (or not visible at least)

The previous versions are in the Retired state. They were selected for Retirement. As per the doc, you will need to create a new article with the same content. It is expected behavior that the Checkout button is not displayed for this article.

Here is some documentation on Knowledge article states:
https://docs.servicenow.com/bundle/london-servicenow-platform/page/product/knowledge-management/concept/knowledge-article-states.html

As per the doc here https://docs.servicenow.com/bundle/london-servicenow-platform/page/product/knowledge-management/concept/c_RetiredKnowledgeArticles.html:
"The article number associated with the retired article is not available for reuse."
"To reuse a retired article, create a new article with the same content, which is published once approved."