Seems so. You can hide both sidebars in the main window by resizing them smaller, hiding icons in the toolbar is also possible.

I think this is the closest I could get the toolbar to match the article on Big Sur.

- There's an unremovable vertical separator, which is related to the new sidebar behavior. - The filter button seems unremovable. - Other toolbar buttons can be moved to the left of the sidebar-related vertical separator, but the flex-space doesn't work the same as described in the article. As a result, the search bar can't be centered.

=> https://media.rymate.co.uk/file/professibly.png