That 'part' only exists in the mind of people with a very limited understanding of warfare.

Even at the time it was obvious that the Russians had no intention of 'taking' Kiev.  At the same time, NATO had to divert resources to face the Russians in the area since they couldn't be allowed to roam about freely.  To many covert biological weapons laboratories and that sort of thing.  So, it sucked Ukrainian resources away from the defenses of what the Russians did intent to take and keep.

This is actually pretty basic stuff.  The Russians do seem to have had some hope that the entire country would collapse during the initial phases of the war and having control of some areas around Kiev in that situation would have been handy.  They also seem to have been prepared with plans for multiple different scenarios...a concept which is alien to low-functioning people.  For instance, if there were resistance in the North they would just pack up and leave, and that seems to be what played out.  Shrug.