The Russians have nearly established complete air superiority. The Ukrainian air defense system is on its last legs. Once that goes, Russia will send in the heavy bombers and do three things - take out the bridges across the Dnipro, take out all of the power substations used to step down their power from their remaining nuclear power plants and then carpet bomb any that make it to the front. Since Ukraine's rail system is almost exclusively electric, it will be come extremely difficult to move the equipment to the East or South. With the bridges out, they wouldn't be able to even if they had power.

Tanks without air cover are just expensive coffins.