An option to use monospaced font when writing

Please, be as descriptive as possible. Issues lacking detail, or for any other reason than to request a feature, may be closed without action.

### What
An option for using monospaced font (Menlo or system default).

### Why
Some people prefer writing using monospaced fonts. It's easier to find typos and to distinguish characters.

### How
Maybe a checkbox or drop-down menu belo “Font size” slider could do the trick? A proper font selection (with all system fonts available, font size in pixels etc.) would be amazing.

Start by locating the macOS writing settings area containing the “Font size” slider and review how its current font preference is applied. Done means users can choose a monospaced font, such as Menlo or the system default, while writing; the requested checkbox, dropdown, or broader font picker remains to be decided.

Written by the indexing model from the issue text.