Note the clarity behind Putin’s actions and their stated rationales. From Andrew Korybko at korbyko.substack.com:

The longer that Ukraine refuses to agree to peace on Russia’s terms, the more land that it stands to lose, which might ultimately be much more than anyone expects if the US soon abandons Ukraine in order to cut its losses.
Putin warned in March 2024 that Russia might set up a “security zone” inside Ukraine in response to cross-border strikes and raids, which it then began to do two months later that May after Russian troops made a fresh push into Kharkov Region at the time. Regrettably, the incursion didn’t penetrate too deeply, and later that summer Ukraine launched a sneak attack against Russia’s Kursk Region. It was only earlier this year that Russia finally expelled all Ukrainian troops from there with North Korean assistance.
Nevertheless, Putin just announced late last week that “a decision has been made to create a buffer security zone along the Russian border” with Belgorod, Kursk, and Bryansk Regions, thus meaning inside the corresponding Ukrainian regions of Kharkov (once again), Sumy, and Chernigov. Unlike last year’s attempt, this latest one might be more successful due to the very different context within which it’s being pursued, particularly as regards the conflict’s new diplomatic and military dynamics.
Regarding the first, “The Devil’s In The Details As Trump Announced ‘Immediate’ Russian-Ukrainian Ceasefire Talks” right after his latest call with Putin, the details of which readers can learn more about from the preceding hyperlinked analysis. Its relevance to Putin’s newly announced buffer zone plan is that his declaration might initially be intended as a form of pressure upon Zelensky to coerce him into having Ukraine finally comply with Russia’s demanded concessions for politically resolving the conflict.
As for the second, it was assessed in mid-March that “Russia Might Expand Its Ground Campaign Into Sumy, Dniepropetrovsk, And/Or Kharkov Regions”, with Dniepropetrovsk being mentioned instead of Chernigov since Russian forces are approaching its border from Donbass after going around Pokrovsk. Crossing that administrative frontier into a region that Russia doesn’t (yet?) claim as its own could circumvent Ukraine’s formidable defenses in central Zaporozhye and lead to that region’s swift capture.