The best way to pin a post is to move it to the Featured Section or Recommend it! As a Host or Moderator, when you click on the three-dot menu of posts in your own Activity Feed on the web, you'll see an option to Recommend.
When you click Recommend, the chosen post will jump to the top of your members' Activity Feeds. The chosen post will move down the Activity Feed with new activity. Between Recommend and the Welcome and Featured Sections, you've got a bit more curation and control over what your members see.
You can Recommend posts in the main Mighty Network, as well as in Groups and Courses.
Updated July 2022