This public vs. private split goes back a ways. When the eastern regions split off in 2014, many Ukrainian political figures took the public stance of recovering those regions at all cost, while privately admitting they were glad to see them go.

From a British political scientist who interviewed them: So...We can imagine that the Ukrainian leadership will continue to voice support for regaining the occupied territories, but not try very hard to actually bring it about. In interviews conducted in Kyiv in the summer of 2018, several elites asserted that while Ukraine cannot declare a policy of surrendering the territory, recent changes in law and in practice indicate a de facto policy of stabilizing the status quo rather than trying to reverse it. (https://journals.sagepub.com/doi/full/10.1177/08883254187910...)

They probably mean that the official stance, as voiced by Zelenskyy on TV and state media, is to reconquer the whole of Ukraine, including Crimea, but everybody knows that it perhaps won't be possible to achieve this ultimate goal.

It's not private, but it is not a secret either. It just isn't the official position of the government.

I think it's good for the morale that Zelenskyy the strong leader of Ukrainians that will repel the bloody Russians whatever the odds, and Zelenskyy the prime minister with a terrible defensive war on his hands, to be two separate personas. One is more personable, but you need the other to win hearts, minds and the war.