There are Ukrainian losses, just not as many as the Russian losses, due to the nature of the war. Russian officers demand their soldiers advance at all costs, resulting in heavy combat losses. Ukraine is happy to slowly retreat, as long as Russia incurs those heavy losses.
At some point, Russia will not be able to sustain the losses. We saw that in 2022, when the initial Russian invasion force of 180,000 was practically eliminated, and Ukraine walked through Kharkhiv and Kherson.