Precisely because Putin in the first month or so beelined straight to Kiev, the capital of Ukraine, in an attempt to surround and cut it off in what appeared to be a siege thus meaning most likely there was an attempt to actually capture the city itself.
You don't capture your enemies capital unless you intend to conquer the country for either regime change and the installment of a puppet or total capitulation and subsequent annexation. A feint attack designed to cause Ukrainians to withdraw from the Donbas seems unlikely as far too many troops died (or rather were sacrificed if one is truly to believe it was a real feint) on the road into and subsequent withdrawal out of a few months later. There is one exception that could make it a legitimate feint attack and I'll explain this lower down.
Also far too many of Putin's military was dedicated from the get go to this attempted capital siege.
Hmm, I wouldn't exactly call it a beeline, the column that headed for Kiev took its sweet time (it got within artillery range to Kiev fast enough, but the column stayed put without deploying its artillery and MLRS for a long time, as if it had orders not to really engage anything seriously (just like all the other forces Russia sent into northern Ukraine in Chernihiv, Sumy and Kharkov which all avoided confrontations, in total this northern advancement likely numbered about 75 thousand troops, but in no way could a large enough portion of them ignore the entire northern front to focus on Kiev to plausibly threaten the city)), as if it were giving Ukraine time to reinforce Kiev with some of their best equipped and trained troops. Also, it is unlikely that the 15 000 troops Russia sent towards Kiev in that long column everyone were focused on would even outnumber the defenders of the city (one really needs a 3 to 1 ratio when sieging and taking a city). I think the main reason why Russia took a land area of the size of Southern England in southern Ukraine (most of Kherson and Zaporizhzhia and Lugansk) in the first three weeks was a lot due to the chaos, confusion, and uncertainty that the northern advancement caused within Ukrainian decision making, they couldn't afford underestimating the Russian troop count there or risk losing the capital, so they were forced to hastily reposition more than they likely needed towards Kiev. About 10 000 Ukrainian troops got surrounded in Mariupol and Mariupol was likely one of the main strategic objective for the start of the Intervention seeing as it was a key city within Donbas which the anti-maidan movement initially had a strong foothold in, and it was the city that hosted the Azov regiment's headquarter, making it a very symbolic city for the DPR. Other main objectives was probably to open the water canal in the Kherson region which supplied Crimea with 80% of its fresh water before Kiev closed it off in 2014 to dry out Crimea (they had to strictly ration water for 8 years); as well as establishing a land bridge between Rostov and northern Crimea. In Kherson Russia captured military bases filled with ammunition and equipment which the Ukrainian defenders had hastily withdrawn from.
I mean, if Russia were only interested in defeating Ukraine fast then they would have launched missile strikes on key civilian infrastructure and decision making centers from day one to paralyze Ukraine, not give Ukraine 7 months to change its mind before doing it. Russia don't want to wreck Ukraine, but there seems to be no other choice available to them, and no, withdrawing is not a viable choice (from the Russian perspective, which is the one that matters when it comes to Russian decision-making) as for example millions of Ukrainians have changed nationality by now, and they face severe punishment if Ukraine comes back which means they would keep on resisting the invasion of western Ukrainians invaders just like they did the 8 years before Russia intervened on their behalf. Seems more like Russia had not prepared anything that could possibly bring the conflict to a quick resolution, while having prepared enough to maintain the conflict for a long time with some confidence.
Therefore in my personal opinion the least risk option would be to attack Kiev foolishly believing one had enough forces to take it from the get go and assume the Ukrainians were a paper tiger similar to the Afghan forces also trained by the United States and they would flee and abandon the Zelensky regime in an instant. This then in turn means overthrow of Zelensky's government was there from the start, which then means that either a puppet regime replacing Zelensky that would be more favorable to Russia or outright annexation by Russia was the intended goal rather than a small scale special military operation.
That might have been a distant hope, as well as there possibility that Ukraine would choose to make concessions akin to the Minsk 2 agreement which they previously agreed to rather than chose war with Russia when it became obvious that Russia was not kidding in regards to the long winded conflict. I agree that Russia had probably a "too good to be true" plan (call it plan A) that aimed for an unlikely quick resolution, but they clearly had plan B's and C's for what to do when plan A would eventually fail. The Ukrainian army can't be compared with the Afghan one though, the Afghan army was just leeching money from the US, it was an good job opportunity for the the impoverished Afghan men from uneducated villages, their commanders were mostly corrupt (and it was not uncommon for them to be drug addicts) and so were the US personnel in charge of building up the Afghan Army, the Afghan Army had shown time and time again that they were not motivated to fight against the nationalists when confronted, that they were mostly hiding behind the security provided by US presence, and had no sense of patriotism and discipline within its rank, seeing itself as subordinate to the US rather than to their own country. The Ukrainian army however was war hardened, extremely nationalistic, disciplined and had been waging war on their own population for 8 years, so these guys were not afraid of confrontations and violence and horror, and Russia must have been aware of Ukraine's willingness to fight having seen their fanaticism on display for years right across their borders (heck, they have practically the same national culture and mentality, both Russians and Ukrainians are known to not back down when faced with conflict, death and violence, they are both corrupt, patriarchic, mainly Christian orthodox and culturally conservative in general).
www.wsj.com
This is where we sorta dive into conspiracy territory, as a willing attempt to deceive (and in a somewhat malicious way) is the only way whereby one could conclude the attempted siege of Kiev was indeed a feint attack. Not a feint attack mind you to cause the Ukrainians to withdraw their forces, but because Putin needed a strategy that would force Ukraine to escalate to such a degree he could politically vilify them domestically so as to convince the Russian people that annexation of all of Ukraine rather than merely securing the Donbas as the only acceptable solution to bring about peace. In other words he intentionally botches the initial attack, gets his own soldiers killed by the enemy to increase domestic anger and use that to justify conscription to gain the numbers necessary for a full occupation and conquest of the whole nation. Remember that Russians before as well as Ukrainians themselves even believed an initial invasion to be impossible as they still believed themselves to be Slavic brothers before the attack blaming local politicians instead for what was going on in Ukraine since 2014, so Russians themselves would not outright be open to total conquest and destruction of their neighbor unless they were willingly vilified through an endless tit for tat escalation whereby they could be convinced that annexation of the whole of Ukraine to be the final solution.
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