The only way to stop an invading force is to hit them where it hurts which is hitting Russian infrastructure on Russian soil.
Look at any other invasion in the history, they never end by fighting the war in the invaded territory. WW2 didn't end because Nazis were defeated in the front-lines kilometers outside Germany or for example the invasion of Yemen stopped the day the armed forces of Yemen managed to attack their invaders' infrastructure inside their own soil (eg. Aramco in Saudi Arabia, UAE airbases and US military bases in the region, etc.).
Putin and his entourage are now in despair and are looking for a worthy way out of the failed war in Ukraine. Russia has several options and they are either bad or very bad for her. Therefore, Putin is simply hoping for a miracle, for a change in the situation in the world in his favor. But the United States and Europe, by making decisions on the supply of their main tanks, have already made it clear that there will be no compromises. Recently, Putin was still given the opportunity to save face in the event of the actual defeat of Russia. The decision to supply tanks to Ukraine (and the issue of F-16 fighters is already being decided) indicates that Putin has missed the last opportunity.
In Russia, the people have been zombified for a very long time by Putin's propaganda, which distorted objective reality, created the image of a fictional enemy and the illusion of the power and invincibility of the Russian people. The problems that arose there were always tried to be solved from a position of strength, or threats to use it. But self-confidence and corruption have taken their toll. The Armed Forces of Ukraine brought Russia back to its current reality. Therefore, they are already slowly beginning to see clearly there. Based on this, the United States, the West, and Ukraine as well, make decisions in stages and in relation to the situation that has arisen. Therefore, it is possible that the Armed Forces of Ukraine will have to operate on the territory of Russia in the future. Already now, Ukraine is striking at military airfields, the accumulation of troops and equipment on the territory of Russia. Of course, Ukraine will stop when there are clear guarantees that Russia will not attack in the future. At the same time, the assurances of false Russia will not be taken into account.