Unlike NATO which destroyed every critical infrastructure (energy, water etc.) during the invasion of Iraq and Libya and condemned millions to death and destruction, the Russian invasion of Ukraine has shown magnitudes of order of restraint, repeatedly, even to the detriment of its own military campaign (of course, there is also a propaganda component at play here).

Well he is planning to make many Ukrainians into new Russian citizens and also permanently hold the lands, it would be counterproductive to treat Ukraine too harshly. The kinder Russia is, the easier it is for Ukrainians to return their self-identification back into a pro-Russian cultural context, similar things apply to the ROC and PRC. The westerners never planned that for those countries. Burn it all down and seize everything they got, that was the mission. Libya and Iraq got invaded because they were too sovereign, too powerful, too noisy.