The lower water level upstream could threaten the safety of an offline nuclear plant upriver.

The plant is in the cold shutdown right now, so while it still need some water as cooling, the amount is way lower than in case of normal work, so even in the worst case of complete dam destruction it will not be affected as it is now.

I can’t tell which side controls the plant, so I’m not sure who that would affect more.

Currently Russia.

Russia could have easily done this to distract Ukraine ahead of it’s counteroffensive and to make the river harder to cross.

Problem is, nobody proven that offensive is even real, not to mention that it was prepared there. Currently the most intensive fights are being waged somewhere else. Also Russia recently hit at least two or three huge UA ammo depots which probably really did hampered any preparations. And the battle of Bakhmut was colossal meat grinder where regardless if we agree on exact numbers, Ukraine lost some of their best soldiers remaining (exactly those who would spearhead the offensive) and Russia lost mercenaries.

Both sides will see flooding but moreso the Russian side because it’s flatter.

Also basically all Russian defensive positions along the river were destroyed, countering the guy above on similar level i could say UA surely hit it because it will make their attack much easier when the flood lessens.

Finally, UA already had plans for exactly that action last year, as they admitted to WaPo: