Same as @Daeraxa, I do not access tags any other way and have been waiting patiently for nested tags to reappear.
That's extremely likely. It depends on how far "removed" it is.
Would it make any difference if the sidebar was tabbed? So the top of the sidebar comprised two tabs; one marked NOTEBOOKS and the other TAGS with the lists effectively sharing the entire sidebar area. Then the list of tags is only generated when the TAGS tab is selected.
Crude mockup below...

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