They apparently weren’t ready for a conventional war....................
Russian military doctrine is based on a land war against NATO and includes the deployment of tactical nukes, not a civil war in Ukraine.
They threw away their military doctrine and tried an American "winning hearts and minds" approach that sought to minimize civilian casualties and destruction of infrastructure, something they've not trained for.
It didn't work out in Kiev. Russia will be forced to switch tactics because they can't afford to lose this war under any circumstances.