Your memory is very short.
Ukraine spent a lot of time last year shelling the Dnipro crossings in Kherson because there were Russian soldiers on the North bank whose supplies Ukraine wanted to deny. They shelled a bridge next to the dam but they scrupulously avoided shelling the dam itself because they knew it would be a catastrophe. Why would they choose to do it now when there are no Russian soldiers on the North side of the river and they might want to cross it themselves?
Not that short - I mentioned this earlier. The Washington Post (slightly more reliable than 'Jay on Twitter', maybe?) ran an article on December 29 2022; here is a quote from it:
"Kovalchuk considered flooding the river. The Ukrainians, he said, even conducted a test strike with a HIMARS launcher on one of the floodgates at the Nova Kakhovka dam, making three holes in the metal to see if the Dnieper’s water could be raised enough to stymie Russian crossings but not flood nearby villages.
The test was a success, Kovalchuk said, but the step remained a last resort. He held off."
https://www.washingtonpost.com/world/2022/12/29/ukraine-offensive-kharkiv-kherson-donetsk/I don't know if this is referring to the holes made in the road bridge next to the dam or as it says, to the floodgate itself. So I don't know if that test strike damaged the floodgate. But what we can learn is that they would have been willing to damage the dam to a such an extent that the river would become a lot wider, in the event that they had no other way to defeat the Russians on the West bank in Kherson. So we can't rule out the possibility that they would, in certain circumstances, deliberately target the dam with the intention of causing damage to it.
Edit: but just as the Russians would be unlikely to deliberately flood their own defences downstream, I guess the Ukrainians would also be unlikely to flood their own positions on the islands in the river.
One other thing we should establish is whether the source in the Washington Post's claim that they damaged the floodgate should be taken to mean the actual floodgate. If it was damaged, this could explain why the Russians apparently had difficulty opening it back in May. It might also support the accidental breach theory