Zelensky announced to plan on taking the Crimea shortly after he was told by the West, that will have to accept negotiations. The West doesn´t believe that Ukraine is able to take lost soil back.. So, in my opinion, Zelensky is promoting overstretched goals to get more weapons. Only weeks ago, Zelensky said the Russians prepare an offensive with 500.000 troops, referring to intel. Apparently, that was not true. If that was true, Ukraine would not prepare an offensive.
My guess that Ukraine only prepares such an offensive under US pressure. They even pulled the skilled troops out of Bakhmut, although even Zelensky underlined the strategic importance of the city.
History has shown that it can be done but it's going to be brute force. Hence the need for at least 100,000 troops, modern weapons and do it very, very soon.