Do Russia's various narrative rationalizations really matter?
As with many things, Russia has a variety of propaganda narratives, crafted for different audiences, but all designed to provide "justification" for what they were going to do anyway. For those inclined to be persuaded by historical arguments, they have a narrative ready to go. For those persuadable by the "de-Nazification" trope, they've got that covered. Same with those who might be sympathetic to narratives centered around Russia as the defender of traditional values against the decadent West. Oh, and I'd be remiss in leaving out the dreaded specter of NATO encroaching on what Russia views as its geopolitical personal space.
Russia really doesn't care if reality and empirical evidence contradict any of these narratives because they can easily switch between them, or play "mix and match" as needed. Just taking history, as one example, if you go back far enough you can make the argument that all of Russia belongs to Mongolia as Moscow was a vassal under Genghis Khan. In addition, Kyiv predates Moscow by centuries, and Ukrainian language, tradition, and culture are senior to those of Russia. Even the name "Russia" itself is derived (some would say appropriated) from the older Kyivan Rus.
During the Age of Empires national borders changed with every significant war and alliance (often by marriage between royal families). Arguably that age came to an end after the World Wars of the 20th Century, although Russia either didn't get the memo or refused to acknowledge it. After the fall of the Tsar and the end of the Russian Empire, Ukraine declared independence and the newly empowered Bolshevik rulers of the USSR (Russian Empire with new branding) fought to pull them back in. Then, after the fall of the Soviet Union, Ukraine declared independence again, but this time Russia lacked either the strength or the will to prevent it. Chechnya was tragically not as fortunate.
From 1991 to 2014, Russia had ample opportunity to lay out any supposed legal or historical claims they may have had with respect to portions of the newly independent Ukraine. Those claims could have been raised in any number of forums, not least the United Nations itself. In stark contrast, there were a number of international agreements and documents in which Russia explicitly recognized the borders of the independent post-1991 Ukraine. In fact, it's telling that Russia entered into a lease agreement with Ukraine that allowed them to maintain a naval presence in Sevastopol. One doesn't lease one's own property. The execution of a lease agreement is an explicit recognition, factually and legally, that the property is owned by another.
One further quick narrative debunking: the so-called NATO impingement and implied threat. It's remarkable that so many who should know better simply swallow Russia's baseless assertion that Ukraine was on the cusp of joining NATO. That assertion ignores the fact that it takes unanimous consent of every existing NATO member to admit a new country. Before Russia's act of aggression in their invasion of Ukraine, they had a firm clique of NATO countries that could be relied upon to block membership. Again, you have to think back to the pre-invasion geopolitical landscape. France and Germany would probably have blocked Ukraine to prevent "destabilization" while Russia-friendly countries like Hungary, Bulgaria, and Slovakia would have blocked membership just because Moscow asked them to. There were other factors weighing against Ukraine but, without needing to get into those weeds, suffice it to say that the whole "Ukraine in NATO" narrative is one giant red herring.
Bottom line: Russia wants Ukraine because that's the only way they can start reconstituting their lost Empire. Belarus is a de facto client state and, if they can get Ukraine, then the Baltics would most likely be next on the agenda. Because the Imperial Mindset is alive and well in Russia, and not just with Putin, it was only a matter of time until the attempt to conquer Ukraine was made. In the Russky Mir view, Russia is entitled to whatever it can take (or retake) by force. Unfortunately for Putin, his sycophants overestimated his strength and underestimated that of Ukraine. That miscalculation may very well result in the downfall of Putin himself and may also be the final nail in the coffin of Russian Imperialism.
Can't happen soon enough, IMO.
P.S. And let's not forget that China is standing by ready to pick up any juicy pieces that might fall their way in a Russian collapse!