The government in Kiev doesn’t need legitimizing. President of Ukraine was elected in a free and fair elections by over 70% of the voters. The dictator of Russia changed their so-called “constitution” to allow himself this post forever and then murdered and/or sent to Gulag all of his potential opponents.
I agree that the government in Kiev is legitimate. But that’s not how the Russians see it. My comment was about why Putin would avoid anything that would confirm such, like a photo of Putin and Zelensky sitting across table from each other as equals. Not an image the families of all the Russian dead and disfigured would be happy to see. But which his rivals would be delighted to use.