How to disable MD edit file side by side preview

Does anyone know how to disable the side-by-side preview for editing .md files?

Recently (in the last month) the edit action for .md files has changed in our on-prem deployment.

It used to be that I could edit in raw markdown, and then select preview and then the screen would change to just the rendered output.

But now, it splits the window such that the left hand pane is the markdown and the right hand pane is the preview.

I hate this. It panes aren’t really large enough to show either well (at least not on my screen display). And so I no longer have a way to cleanly preview my changes, without excessive word wrapping, or scrolling.

I can’t see this sort of customization in the repository settings. And I don’t see an on screen flag, button or option to use the full screen preview.