Why did Germany and France oppose Ukrainian admission to NATO? Because they accurately predicted the consequence. There's no other reason.
So Putin LITERALLY had nothing rational to worry about, unless he gave the likes of Ukraine, Sweden and Finland, an existential reason to join NATO that they’d never have if Russia wasn’t being the aggressor.
That was still true until the coup, and the coup government then put NATO ascension into their constitution. Even that wouldn't be a particularly nasty problem for the Russians, except that NATO after the fall of the Soviet Union was no longer simply a defensive alliance. It was used as an international imprimatur to attack and partition Serbia (coincidentally, a historical Russian ally) and to assist jihadists in regime change in Libya. In neither case was NATO involvement the consequence of 'defense' of the members.
This is why the “don’t poke the Russian bear” anti-NATO-expansion stuff was utter nonsense on stilts.
There are hundreds of thousands of people now dead who might characterize the dangers of provoking Russia differently, if they could still speak.
The neocon NATO expansion has only achieved the war NATO was supposed to prevent. Utter foreign policy failure.
This CSPAN clip from June 18, 1997 better than anything highlights how poorly neocons predict the outcome of their actions:
In the clip then Senator Biden mocks Russia and says of their opposition to eastward NATO expansion, 'what are you gonna do, ally with China and Iran? That's not an option.' Well, here we are...
But it's academic, because Ukraine AGREED with that! Prior to 2014, Ukraine never applied to join NATO. The only reason it has done so since 2022 is because Russia has serially violated decades of non-aggression agreements against Ukraine, border recognitions, formal UN and Belovezha recognition of Ukraine's "independence, sovereignty and territorial integrity" all in order to force vassal state status on its neighbor for the Greater Glory of Russia. What did they think Ukraine was going to do? Accept the "ratchet effect" of Moscow's serial abuses of power and influence, its serial breaches of contracts and faith indefinitely?
That was still true until the coup, and the coup government then put NATO ascension into their constitution.
Again you're mistaking effect for cause. Ukraine's NATO ascension was not the cause of Russian aggression; Russian aggression was the cause of Ukraine realising that all it was actually getting out of Russia in return for its "neutrality" was Russia bullying and blackmailing it. Even when Russia and Ukraine were both in the NATO partnership for Peace, Russia tried to assassinate Ukraine's presidential candidates on the basis that it didn't want Ukraine to have even the same relationship with NATO that Moscow itself was actively promoting. Come on, dude; make that make sense.