One of the main reasons for the war in the first place was because Ukraine was becoming too much of a rival to Russia in terms of Oil and Natural gas being sold to Europe.
Russia had pipelines that went through Ukraine. Before the election in 2014, the leader of Ukraine was effectively a puppet that would do whatever Putin wanted. But after Zelensky was elected, they decided to stop letting Russia use that pipeline for essentially free. Also around that same time, a bunch of surveys were conducted in the Economic offshore zone of Ukraine and they discovered a bunch of oil and natural gas reserves. Ukraine with their current infrastructure, had no way to extract said resources so they turned to American oil and natural gas companies for partnerships to extract them.
Russia didn't like this. They also wanted Sevastopol back firmly under their control so that's why they took Crimea. By doing so, they effectively took control of roughly half of these new deposits. Also some of the contested areas in eastern Ukraine have rare earth metals.
Putin can say as much as he wants about Uniting the former Soviet Union, but ultimately this is about resources and money.
I watched these videos years ago when the conflict started and they're still relevant.
RealLifeLore and CaspianReport have some great videos and they've continued to put out really great content that goes behind the deeper geopolitics. Obviously watch, but verify claims.