• Move the public box to the middle of the editor, then add the preview portion for the subscriber-only post above the public box.

If you want it to be viewable only after subscribing to the channel

  1. Move the public box and set the limited public portion
  2. Publish > Visibility settings: select "Visible to subscribers only"

Subscribers can see the full content of the post, while non-subscribers can only see the preview portion (the content above the public box).