Always weird to see one of these Russiansplainers pop up.
As a wider point, outlining long-held academic explanations of Russia's motivations is important.
Explaining is not justifying. Russia is a dwindling force with terrible geography, and is only kept in it's current position in the world order because of its abundance of natural resources, nuclear weapons and shady international influence. With the move to carbon neutral and a terrible demography, already paranoid Russia, whose population still perceives itself as a major world power, will become more and more aggressive.
Russia has therefore invested billions in developing and leasing warm water ports. It invaded Crimea almost immediately after their lease on Sevastopol was threatened. It is well known that it had been moving Russian-friendly individuals into the area for years, due to its paranoia about losing its grip on Ukrainian government stooges and thus Sevastopol.
I didn't think it needed to be stated, but it does not excuse Russia's actions in the slightest. You obviously should not invade countries, kill and torture tens of thousands of people, and destroy their homes because geography doesn't favour you. It is inhumane and barbaric. Even from a purely Russio-utilitarian point of view, probably ultimately futile without a huge geopolitical shift
My specific response was that Russia has, and will go to extreme lengths to retain Sevastopol, due to its strategic geographic importance. I don't think that will result in the use of nuclear weapons, as that will lose Russia some of the few friends it has left, but it could result in conscription/ proliferation of the evils we have seen so far