I came here to log a similar request and found this one. Having a vertical monitor for documentation sites, I find Table of Contents sections hinder more than help.

I find using a vertical monitor for documentation is a more natural for reading, as it more closely resembles a traditional paper page. More of the page can fit on a screen at a time. Vertical scrolling is reduced.

A table of contents sidebar, however, hides content on vertical monitor setups requiring side-scrolling. Additionally, since the table of contents takes the entire height of the screen, it frequently takes up more than twice as much space as it puts to use.

Adding the ability to collapse the table of contents, similar to how the main sidebar is collapsible, would improve the readability of Docusaurus sites on vertical monitors.