Ukronazi

What's this neologism? Are you not aware nazis are very well integrated in the State apparatus in many nations? It's not just Ukraine: it's also Russia, France, Germany... So why paint a single nation as nazis when more or less of all the parties involved in the conflict are varying brand of imperialism and racial/cultural supremacy?

supporting a planned Ukronazi attack on Donbass republics

What's the evidence that there was a wide-scale attack planned? If that was true, it could justify bringing military support to Donbass as an incentive for the central government not to attack, but how could it ever justify invading the rest of Ukraine?!

Russia also offered diplomatic solutions many times (since December, and in fact since 2014).

From this article, the demands formulated by Russia amount to saying eastern european countries can't have military alliances except with them (neocolonialism, much?). Interviewed russian foreign ministry says:

This is not about us giving some kind of ultimatum, there is none. The thing is that the seriousness of our warning should not be underestimated

That's not a diplomatic solution, that's extortion/bullying. "Do what i say, or else..." has nothing to do with diplomacy and nothing to do with the political autonomy of specific regions.

just a few days ago Ukraine threatened to develop nuclear weapons. That was obviously a red line for Russia

Iran did pursue to develop nuclear weapon for decades. Has that ever justified a full-scale military invasion from the USA? Oh yes, the USA fascists and hard-liners from the republicans would have loved that. Just like the various fascists, traditionalists and neo-nazis of Russia who love the flag and the military really love the idea of conquering Ukraine and reforming a Great Russia (like historical nazis liked their Great Germany). I did not think i would ever say this in my entire life, but do you realize you're spitting propaganda from actual fascists in the name of fighting against nazism?