I have one Layout page on my site. I would like to delete it but I do not see a way how in the admin UI.
My web searches have turned up nothing. I guess you might say: just disable it; but I would actually like to delete it.
I assume this is possible because I have another Backdrop site that has no layout pages.
That one is provided by (I believe) the standard install profile. You may not be able to remove it through the UI. If you install the minimal profile it won't pre-install this layout.
On a dev environment you might try removing these from the active config folder and then clearing caches: