See the empty space on either side of the document. And as I said zooming in does not change the width of the editor so I am forced to squint at smaller type if I want to see what it actually looks like on the page.
For the main editor, is it possible you have ‘fixed width’ enabled? (File > Options > Appearance > Main Editor > ‘use fixed width editor’). Disabling this option should allow your editor to fill the full space, if it’s functioning properly in your version.
For Composition Mode, there should be an option to expand the editor to fill the whole screen on the bottom menu – if the menu isn’t visible, drag your mouse to the bottom of your screen and it should come up. If you draw the ‘paper width’ slider as wide as it’ll go, that should fill the screen for you.
You can change the transparency of the background in Composition Mode by hovering your mouse at the bottom of the screen and using the control on the bottom right (Background Fade).
From your screenshots, the last method looks to be the one you should try first.
