First of all, spoils of war doesn't work the way you think it does under international law, according to multiple treaties to which Russia is a signatory. Spoils of war are limited to military equipment like tanks or ships. You can't invade your neighbor and declare anything you can grab as yours because they're spoils. Private property, civilian infrastructure, cultural objects and human beings are explicitly excluded.
So when Russia seized the power plant, what it got -- again according to treaties it signs and holds other countries to -- is a mess of responsibilities. It is obligated to protect and maintain the plant. It is obligated to protect the civilian population in the areas under its control, both by maintaining the plant in a safe condition, and by providing normal infrastructure services to those civilians; it does *not* however, need to ship power to the rest of Ukraine.
So Russia could, under its treaty obligations, sever the grid in the area around the plant from the rest of Ukraine, and connect it to Russia. The plant would then provide normal services to the civilian population in the occupied area, and also provide power to Russia at least until the final status of the province and power plant are agreed to by the belligerents.
What Russia can't do is use the plant, in essence, as a giant dirty bomb to blackmail Ukraine. That is a war crime under the Geneva Conventions. But so was destroying the Kakhovka Dam back in 2023. That's a cautionary tail, because it tells you something important: the Russian military leadership aren't just war criminals, they're idiots. The consensus was the intent of the dam destruction was to hamper Ukrainian movements. But it also hampered Russian movements. What's more it cut off the main water supply to Crimea, which Russia considers Russian territory. This caused massive economic damage to the man industry in Crimea: agriculture. Not counting environmental costs, and the billions of dollars required to build new wells and desalination plants, this act by Russian generals is costing Crimea, a "Russian territory", tens of billions of dollars a year economically.
So the takeaway is this: the fate of the Zaporizhzhia Nuclear Power Plant is in the hands of idiot criminals.