The answer is simple: EU and USA taxpayers billions pumped into Ukraine to buy hundreds of thousands of mobile diesel powered generators and fuel for them, and spare parts and replacement blocks for everything that’s been destroyed.

On top of that, Ukraine inherited a lot of nuclear power plants, and despite losing the largest one in Zaporozhie region, still operates all the other as Russia doesn’t attack them in any serious way.

No miracles, just pumping money non stop.

Maybe because it has not been privatized, yet?

https://en.m.wikipedia.org/wiki/Ukrenergo