seems to be to create a giant pincer to north and south, with Russian forces stuck in between.
If the Russians retreat quickly in the north, they can cross the border. But if they linger, the Sea of Azov will block their retreat and they will have to find their way to Crimea.
Putin's lesser aim and object of the war, once it was clear that taking all of Ukraine was impossible, was to own the coast from the Don to the Danube.
But Odessa was beyond his army. And now it looks like Kherson will be liberated. The risk for the Russians is that they will lose Sevastopol, where their fleet had a lease. And that will be terminated, of course. Assuming Ukraine takes back its whole country, Russia is short of a place to park its ships and will even be worried about the estuary of the Don river.
Huge disaster for Russia. But we've found out that in spite of losing the Cold War, there's an ugliness and condescension in the Russian character which survived. Any peace treaty should involve the reduction of Russia's conventional military and the limitation of their nuclear arsenal to defensive purposes only. Whatever was done to Germany after WW2 to make them a peaceable country, we want that for Russia.