It’s taken me a while to get back to this, but I finally tried it today. Unfortunately, it doesn’t seem to work correctly for me. While on the “Edit announcement” page for an announcement, clicking on the Preview button opens the admin dashboard page, but shows no Announcer notification bar. I tried with Firefox and Chrome browsers.
When I hover over the Preview button, it shows /wp-admin/post.php?post=3712&action=edit#
When I click on the Preview button, the preview page loads into another tab and the url is /wp-admin/?ancr_preview, and the content of the displayed page is the same as wp-admin/index.php. The Announcer Notification Bar never appears.
However, publishing a notification bar still works normally using version 5.0.