I would say, it would be just a nod "it's ok" to Moscow, since they don't really lose anything personal there.
You Americans are used to the idea of a shared agency, that rulers care for fates of their underlings, let alone soldiers.
I would say, anywhere outside of American culture, few elites will ever care more about underlings than, say losing their Rolce & Royce, or their luxury apartment.
There been no point in this war when Putin was more visibly upset & discombobulated than when his yacht was seized in Italy.
Also, he traded 6 super valuable UA commanders + 250 soldiers just for his personal moneyman.
As a Chinese, I have no ability to interpret him as Americans do, but I believe, where you see some high matters like him trying to repay historical injustices, spheres of influence, etc, I see just him doing ultra-commercial mindset things like risk/reward measuring, hedging his bets, going for risk free moves, moving out of assets soon to be illiquid.
Not just nuke, but almost everything else is a bluff from the beginning addressed exclusively at USA, because nobody else, even Europeans, would've understood it, let alone believed in it.
His interest now is to get out of Ukraine, while recouping at least some losses of reputation, and long term money. This is why he keeps doubling his bets, in hopes that one relatively big victory can cover all his previous losses, and I mean losses to him personally — reputational, financial, social, material.
Putin only went for this war because he was 99% sure that he would lose exactly nothing personally even if his army gets smashed. The West has done almost everything in its power possible to render Ukraine as an irresistible risk free adventure with enormous reward hanging in front of him.
Even if NATO will waltz into Ukraine now, and turn every russian conscripts to the last one into kebab, Putin & Co. will still be able spend the rest of their days living in golden palaces in Moscow, surrounded by hordes of likeminded court nobles, like Kims do.
Nuking Moscow would be the most appropriate.