I don't think Putin has just one goal. He has several goals, some of which seem legitimate (Crimea in Russia, Donetsk and Lugansk independent), some are perhaps dubious, but perhaps negotiable (Ukraine doesn't join NATO), and some are completely unacceptable (e.g. Ukraine should become a vassal state of Russia).
The best approach would be to talk to him, while not coming completely empty-handed (as the West usually is). For example, they might say:"OK Mr. Putin, we are sorry, we made a mistake, what about a recognition that Crimea is Russian, and that the two republics are independent. What this be enough to stop your 'special military operation?' ". I think this would be a good start for a useful conversation.
Of course, should Putin somehow agree to withdraw his troops now, this offers no real guarantee for the future, but a method which has worked now might work again later.
There seems to be a very scary inability of the West to make any concession right now, that's not a good thing.