Russia lost. There were objectives set at the start, and they are no longer capable of achieving them. Russia lost this just as much as the US lost Vietnam.
Crimea can be starved out, and Ukraine is close to getting what they need to do this. They need to be within 75mi of the M14 highway (plus a few more miles because you don’t want artillery to be right at the front line). From there, they can hit all supply lines headed west, which would include all of Crimea. The Ukranians have sent missiles into the Kerch bridge before and can keep doing it. Airplanes can’t keep the whole of Crimea supplied, and neither can the Sevastopol docks.
So basically, wherever that incursion is that keeps a <75mi range to the highway, everything to the west of that is no longer viable for Russia to hold. It might take a while to starve them out, but it can’t hold forever. Putin can choose to acknowledge this and pull out, but he’s more likely to take the Hitler solution of demanding every soldier fight to the last in order to save his own face.