Design the switch from fixed with to full width for the page content

Currently, Cristal displays content in full width up to a predetermined viewport width (~1200px).
Then, the width of the page content is fix to this maximum value.
The advantage is that it limits text line length, which is optimal for reading (source needed).
But, under some scenarios, users of large screens might want to use the full width of their devices to view more data (e.g., a large table).
In this case, it could be interesting to be able to switch to a display mode where all the available viewport width is used for the page content.

Design questions

• location of the switch button
• is the page display mode global to all pages or to individual pages?
• is the page display mode global to all users or to individual users?

Inspiration

Notion provides that option and places it in what we would call page actions.
The setting is local to an individual user for an individual page.