@davidelawrence: seeing the answers you got so far, I may misunderstand your question. Nevertheless, I am taling that risk of giving you an answer to a non-issue.
In the hotkeys section, filter on “vault”, and you’ll find the “open another vault” for which you can set a hotkey yourself.
I only discovered it a few days ago, a godsend, because, like you, I was fed up having to click that button so I dug a bit. That is probably one of my most frequently used hotkeys.
So, if this is not what you’re after I apologise.