Big Sur toolbar item in the sidebar

In "Adopt the new look of macOS", it mentions the ability to place a toolbar item in the sidebar, but I haven't been able to achieve this.

I have a three-pane split view with the left split view item having the sidebar behavior. The window controller acts as the toolbar delegate, passing three items as default identifiers: [.toggleSidebar, .sidebarTrackingSeparatorItemIdentifier, .rightSeparator] where rightSeparator generates an NSTrackingSeparatorToolbarItem between the right-most two panes.

Since .toggleSidebar comes before the separator, I understood that it should be placed over the sidebar when expanded. However, it stays to the right of the separator. Is there some other configuration I'm missing to achieve this?
Hi sean.rich.dev,

Did you find a solution? I'm facing the same problem. The tracking separator doesn't seem to "track" the sidebar divider and therefore the toolbar items don't align as they should.

Thanks.
One workaround I've found is to toggle the isNavigational property on the toggle sidebar item to false (in the toolbarWillAddItem(_ notification: Notification) callback). This seems like a bug.
Big Sur toolbar item in the sidebar
 
 
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