But main sell of the russian side is how they are “protecting russians” in donbass/luhansk and now kherson/zaphirizhia areas.I will say, it has been Russian aim to garner domestic support to continue on with this war, not the Ukrainian. Not saying the Ukrainian can get away with more destruction on their own city, but there are "Allowed" to devastate their own city in a way that it will not get their own population riled up. So if they need to quickly move into a place, they can afford to level it and move in, they can't do it many times but there are leeway there.
Russian on the other hand, needs every support they can get to keep this war going, it's one thing they are attacking and they can shield their civilian from the horror of war but they can't cover the fact that their soldier is not coming home, family member are going to know and they can't really suffer 50k death a year, which mean if the war drag on, the propaganda side in Russia is a lot more concerning than the Ukrainian.
Russia would therefore need to focus on how this war is clean, doing humanitarian works, things that justify the number of losses to a point, what Ukrainian did to their own don't really sell to the Russian people, it has less of a value to domestic propaganda. Ukrainian on the other hand, can spin what happen on their own soil to whatever they want, they were attacked, Ukrainian want the Russian gone, want the war to end, and how it ends does not really concern Ukrainian that much, plus I don't think Ukrainian would digest Russian propaganda that much anyway.
Ukranians leveling kherson and donbass city will provide perfect propaganda for the russians. Showing the destruction and civilian casualties.
I think ukraine is taking this (what effect their action would have on russian war fatigue) into account. Showing restraint striking into russia, and showing restraint with collateral damage. Which is strategically sound.