To be clear, the Esc closed the popup also in the old browser extension UI.
I think that what is really bothering you is the new behavior that remembers the last open view in the browser extension.
My own proposal is to remedy this problem by making available a
Home button at the top of every page.
In the meantime, one work-around is to click on a different browser tab, then click back to the original tab. This resets the UI “memory”, and allows you to return to the original Vault view.