Kiwizoom

This problem was fixed with this little-known plugin which creates a working draft of a published post that does preview, then inserts changes on publish.

https://www.ads-software.com/plugins/live-drafts/

https://www.ads-software.com/support/topic/preview-mode-for-already-published-postspages?replies=6

Another example of the same problem.
Cannot preview changes to a published post.

https://www.ads-software.com/support/topic/editing-and-previewing-posts-after-publishing?replies=4

Changing to draft and then editing, previewing and publishing is a possibility that I don’t want to get into, because it will mess up the dates and thus the order of the post readout.

I have to make the process as simple as possible for the target users.

Nevermind, I fixed this by completely destroying the theme headerfile.

Who knows what this will mean for the future

*stares misty-eyed off into the distance like some romantic crap from the leatherstocking tales*

Change of direction:

Black bar may not be what WP calls an image.

Ergo, new mission: get rid of entire header on website.

My view.

No buttons to be seen

Admin area
Appearance > header
Version 4.0.1

help dropdown:

If you don’t want a header image to be displayed on your site at all, click the “Remove Header Image” button at the bottom of the Header Image section of this page. If you want to re-enable the header image later, you just have to select one of the other image options and click “Save Changes”.