Ukraine is indeed making those claims because they think they can do it. But you were implying this was a Western move, which it is not.

But frankly fuck them. If Ukraine can gain fire control over the bridge to Crimea then it's just Kherson City all over again. Crimea would be immensely expensive to hold. No practical logistical support for what is, by far, the most valuable part of Ukraine. No safe harbor for ships in Sevastapol. Maybe Russia tries to play it out. Maybe they just acknowledge it and give up. But it'd be relatively easy to lay siege to it if the land bridge is captured and the bridge bridge is in fire control (or destroyed). They don't need to march into Crimea itself. Just hold that siege and Russia will eventually need to yield.

Crimea isn't a side objective. It's the checkmate move. It has the potential to be a lot less bloody than fighting for every meter of land in the east.