So far Russians are under performing. Weather that's their overall strategy its hard to say. Maybe they are waiting to amass troupes in large concentrations.
They haven't won a single town in 6 days. Their troupes and equipment are mostly stuck in these long convoys that can easily be attacked. They are overstretched in many in 4 - 5 different areas. Social media shows lots of destroyed Russian equipment as they try to enter cities in lightly armoured vehicles, without tanks or artillery support. Even just 10 - 20 of these Mig-29s can change the tide because they would open skies for Ukrainian drones to attack supply columns. There isn't much of evidence that Russian troupes are receiving any air-support etc.
Putin possibly left it too late in the year. The spring thaw is underway turning much of the territory of Ukraine into a literal quagmire. Russia's armoured vehicles have become stuck in this.
The Russian Air Force is conspicuously absent. When the US invades a country over land, when it is going to attack a country which it doesn't like, the invasion is preceded by weeks of aerial bombing, and the achievement of total air superiority. The following link goes into some explanation for the absence of Russian aircraft in the conflict:
https://rusi.org/explore-our-resear...ary/mysterious-case-missing-russian-air-force
In short, a speculated depleted supply of precision guided munitions, potential inability to operate effectively in the presence of friendly SAMs, and poor training and operational effectiveness of VKS aircrews due to the limited number of hours they are able to fly every year.