People familiar with Russian military and diplomatic strategies said early on in the Ukraine-Russia war that Russian goals would be a moving target. As Russia has taken territory in Ukraine, it notches up the pain level and seeks more territory. From Dmitry Trenin at rt.com:
Putin’s latest comments reveal that Moscow’s thinking has shifted and compromise is no longer on the agenda

Last week, Russian President Vladimir Putin referred to Ukraine as an “anti-Russian enclave” which has to be removed. He also said that the Russian soldiers taking part in the military operation there were fighting for their “own country.” These statements carry important implications.
Over the last six-plus months, the mantra of the Russian officialdom has been that all aims of the offensive will be reached. On purpose, however, the specific objectives, such as how far Moscow’s forces plan move into Ukraine, have never been spelled out. This cannot but raise speculation about what the Kremlin is actually hoping to achieve.
The only person who can authoritatively answer that question, however, is the president, and second-guessing him makes no sense. Yet, two things cannot escape close attention. One is the radicalization of Moscow’s position on Ukraine as a result of both Western policies and Kiev’s actions; two is the widening gap between the minimum result of the military campaign that Russia can be satisfied with, and the maximum amount of what the US and its allies can accept.