Well, they did, apparently it happened days ago (3 days ago) immediately after Ukraine took Kherson.
They are squeezing the Russian from both side and there is rumour backed up by video on telegram that Ukraine breached Oleskhy and Nova Kakhovka, both video were not confirmed by both Russian and Ukrainian source.
The problem for Russian is, either way, whether or not those troop in Kinburn success or not, the Russian aim from pull troop in Kherson so they can be redeploy to the East, if this happened, that mean those troop aren't going to the East and instead they need to stay and fight in Kherson, on the other hand, Ukraine can redeploy bulk of their Kherson assault troop anywhere they want, now that they took Kherson.
They don't need to succeed, they only need to delay Russian long enough not being about to use those troop and reinforce the East, that give time the Eastern offensive to mount. Which is already underway.