This thought just occurred to me as I glanced over a notification that came in on another thread ("...there does not seem to be a way of seeing exactly which layout is in action for a page, even by inspecting the code." Source)
What about a new little icon in the admin menu that either links to a separate page or has a little dropdown info pane with details about the current page you are viewing?

For example, all in one place, info (and potentially links to edit/adjust) about the:
- Layout used on this page
- Theme
- Content type
- etc.
That may be overkill but thought I'd throw it out there to see what people thought.
Recent comments
Oh thanx ! I had an "old" text format that I had disabled. I re-enabled this format in the field body with the permissions and the field comes back for editing.
Problem of access to the body field with a simple post
See https://github.com/backdrop/backdrop-issues/issues/7148
Problem of access to the body field with a simple post
I used the theme gin for admin. Perhaps, it's the problem ? I have a color border when i selected the images and of course i used the "ctrl" key.
Small problem with multi import files images.