Interesting piece of the puzzle I wasn’t aware of: while Ukraine was technically a significant nuclear power, the Ukrainian government never had full control over them, nor the ability to launch them. From Wikipedia:

While all these weapons were located on Ukrainian territory, Russia controlled the launch sequence and maintained operational control of the nuclear warheads and its weapons system.

https://en.wikipedia.org/wiki/Ukraine_and_weapons_of_mass_destruction

In the nineties, Ukraine would have come out looking quite hawkish to somehow wrest control of the weapons and then keep them for their own security. It would have prevented invasion perhaps, but it didn’t seem reasonable at the time.

I do think they have a uniquely legitimate right to hold nuclear weapons in self defense. Without them it’s war until the bitter end - of them or Putin’s regime.