There are plenty of things they could attack. The bridges in the Dnieper are still there. If they wanted to be real nasty they could start blowing up water treatment plants.As others have pointed out, Ukraine has no valuable assets (left) for Russia to attack.
Then there are the nuclear reactors, the oil & gas pipeline pumping stations, underground gas storage facilities.
It will probably happen eventually.Elimination of AFU leadership will greatly silence the propaganda coming from the AFU side.