I don't believe this should be collapsable and take up so much space. It can be a simple row with the icon+name of your site

Collapsable makes sense for a section like "following" which contains many items. But this whole "my site" text takes up a lot of space so we might as well make it "expanded" by default and make it much smaller

For now, I think we should just move this to the top of the sidebar, above or below "my site"

This can go away because drafts now appear in the place where they will be published

Moving to a new account dropdown in the top right, which gives access to settings, profile, and switch account. This design is not yet final so we need to figure that out alongside this project

These are the things the user really wants to save to personalize their space, so I think we should just show them inline. If users don't like the bookmark taking up space in the sidebar, they can delete the bookmark, move it to the bottom of the list (when we support bookmark order one day). And they can put a bookmark inside a bookmark group/folder one day, so the user can introduce more organization.

My suggestions:

Add a horizontal separator because right now the collapse section titles (like Following and Joined Sites) appear very similar to the sites/profiles/docs. A horizontal divider will help the eye understand more quickly.