I scoured the internet and found an interesting article about Russian strategy in Ukraine.
colonel-general-sergei-rudskoy/
Basically the strategy is to block these big cities (Kherson-Sumy-Kharkov-Kiev-Mariupol), arrest the armies that are defending there, stop the sending of supplies from the west to the east, where there are about 60 thousand soldiers heavily entrenched in the Donbass and leave them isolated.
(Sergei Rudskoy) "There were two possible courses of action.
The first is to limit the territory only to the DPR and the LPR within the administrative borders of the Donetsk and Lugansk regions, which is enshrined in the constitutions of the republics."
"But then we would be faced with constant feeding from the Ukrainian authorities of the grouping involved in the so-called joint force operation."
"That is why the second option was chosen, which provides for actions throughout Ukraine's TERRITORY with the implementation of measures for its demilitarization and denazification.
The course of the operation confirmed the validity of this decision."
In theory, until securing the separatist areas of the Donbass region, they would attack all fronts, keep cities surrounded and without effective support from western Ukraine. Almost a distraction to not have heavier resistance there...
The problem is that apparently there was a deliberate or unintentional failure of Russian intelligence and the invasion is taking much longer and more costly than the Kremlin anticipated.
"According to US and NATO secret services, flaws in the interpretation of spy information that led to underestimating the Ukrainian Army would be behind Putin's purges of the FSB and the SVR, the Russian counter-intelligence and foreign intelligence services."
"The failures in the transmission of strategic information and the distrust within the Russian secret services constitute a threat to Putin himself. The distrust parallels the president's pressure on his circle, which, for example, led this week to the escape of Anatoli Chubais."
"Chubais fled after the fall of the intelligence chiefs. There was the public humiliation that, on the eve of the invasion, Putin inflicted on Sergei Naryshkin, head of the SVR. Days later, the head of the 5th Division of the FSB, Sergei Beseda, and his deputy, Anatoli Boluj, were put under house arrest"
"Beseda was in Ukraine in 2014 to help Yanukovych stay in power and did not do well in this task. It was reported that Beseda's arrest was due to embezzlement of military funds. The real reason would have been the absurd report about the real power of the Ukrainian army"