Background colors and widths to be user-selectable for each of the vector 2022 spaces:

• article
• small vertical empty bars on left/right (equal in size to the toggle icon)
• left bar - ToC/service menu (see https://www.mediawiki.org/wiki/Talk:Reading/Web/Desktop_Improvements#Lack_of_left_border)
• right bar - mostly empty with account/login on top
• left unused - to the left of the left bar
• right unused - to the right of the right bar (toggle icon goes here)

For non-logged-in users (via cookie?) - remember line width/ToC position (show/hide)/etc. (as many preferences as possible - almost everything a logged-in user has, including choosing "vector 2010", etc.) - both a set-by-user "global" setting and set-by-user "specific page exception" settings

I would show the toggle always, regardless of window width - but on smaller than some threshold (1400px ?) - the toggle should ALSO hide the ToC menu.