Actually, I found such a button to go back to the old version! It's at the lower left of the window, all the way at bottom, and I use it all the time now:
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Thank you! Came here looking specifically for how to do this. The new UI precludes several of my favourite shortcuts, like typing the origin in the destination to get them to switch, which is useful when I have a list in one field. It looks fine, maybe better, but it requires too much clicking.