Here's a screenshot of a collapsed sidebar:
https://storage.googleapis.com/support-forums-api/attachment...
and a screenshot of an un-collapsed sidebar:
https://techcrunch.com/wp-content/uploads/2019/02/RC-Convers...
It took me some time to realise out that it is the hamburger-menu-like icon in the upper-left corner. It has a tooltip that says "Main Menu", but it is not a menu. It controls collapsing of the sidebar. Confusingly, it is positioned in the top panel, separated by a line that would make one think it is not related to the sidebar, and closer in affinity to the logo, search box, etc.