It is quite sad how often I end up having to help older relatives with their computers on account of unintuitive UI. One memorable, recent example was my mother, who could not figure out how to get her GMail sidebar to un-collapse itself.
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.
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.