Where's the Main Editor now?

I haven’t used Scrivener in a while, and am looking for the Main Editor.

I’ve got this same issue: https://forum.literatureandlatte.com/t/way-too-much-white-space-why/38866/1

I’m looking for this setting:

Preferences > Appearance > Main Editor – untick the ‘Used Fixed Width Editor’ option.

Anyone know where it is?

Here’s a screenshot of the Preferences dialog, with the tickbox highlighted:
[attachment=0]Screen Shot 2020-10-04 at 12.36.16.jpg[/attachment]
Hope this helps!