No one has a right to join NATO.

Whether they have a ‘right’ to it or not is irrelevant. We live in the real world, and in the real world they can’t, anymore than Mexico or Canada could have joined the Warsaw Pact, or invite the Chinese to establish military bases on the US border.
And in reality, no-one is willing to die to join NATO. It’s not an ideal or a freedom, - it’s nothing. But it was a way for far-right Nationalists/Nazi’s to gain US funding and support, and then to gain power, and then to instigate the war with Russia that they had long desired.
And if it sounds crazy that the Ukranian far right would desire war with Russia - well, they’re fascists, they are crazy.
I’m not saying Russia’s actions are ethically correct, but if you look at it from a realist perspective, they are not only understandable but they were entirely predictable.
I don’t believe the Ukranian people wanted war with Russia, but a majority of people in West Ukraine did get caught up by fascist propaganda, and they trusted the far-right to lead them, and now the fascists have left their country in ruins.

The Ukranian people wanted to join NATO

No they didn’t. It’s part of the reason so many Ukrainians especially in the east and south of the country started movements to try to gain independence from the fascist Ukrainian coup government.

The reason was safety and their fears have been justified by what has happened.

The reason was not safety and hundreds of thousands would not have died needlessly in a proxy war if the fascist coup government had not been installed by pro-NATO western powers. Most Ukrainians were not so stupid as to think striving to join NATO was anything but a road to war, which is what has happened.

And NATO would never invade Russia anyway due to its nuclear umbrella.

No shit. That’s why they’re using Ukraine for a proxy war.

And why would they want to anyway?

There are many reasons they (US/NATO/"the west’) want to destroy Russia as it is. They want another comprador government in Russia that is subservient to their interests, not an independent and powerful state that could become an economic competitor (or at least a major component of an economically competitive bloc). They want to exploit Russia (much as they did after the fall of the Soviet Union) by privatizing everything and selling it off for a pittance to American bourgeoisie, just as they have done and are right now doing to Ukraine. Another way of phrasing that last point would be to say they want unfettered access to Russia’s resources (natural resources, labor, etc.) on their terms, not in terms of the national interest of Russians. They want to want to prevent a multipolar world and maintain their global hegemony. They want a government in Russia they control to put further pressure on China. They want to prevent Europe from buying its energy from Russia so that Europe is entirely dependent on the US for Europe’s continued existence. That last one they have already achieved by destroying the Nordstream pipeline, just as Biden promised he would.

And the rebels in the Donbas are and have always been aligned with the Russian agressors, and against Kiev. Remember they used to fight the Ukrainian army even before the invasion.

Everything you’ve said here is a point against your position (of Russia and the people of Donbas being the aggressors), not for it. First of all, “always” should be replaced with “since 2014.” Think about what you’re saying, “the rebels sided with ‘the aggressors’ even before ‘the aggressors’ did their ‘aggression’!” If some kid on a playground, kid 1, starts beating the shit out of a smaller kid, kid2, and a third one, kid3 steps in and punches kid1 to stop him from killing kid2, would you say “kid2 always sided with the aggressive kid3”? If so, you’re a fucking idiot. I guess the people of the Donbas should have just allowed neo-nazis to ethnically cleanse them? They should have just been ok with scores of union members being burned alive? They should have accepted laws that banned their language and made them (at best) second class citizens? And Russia stepping in on their behalf makes Russia the aggressors, not the fascist coup government waging an ethnic cleansing campaign?