As of now at the end of March 2022, it is quite common to find articles in the media and also some declarations by world leaders talking about a food crisis caused by the Ukrainian war. Here are some random examples from a quick internet search:
French President Emmanuel Macron warned of “an unprecedented food crisis” following Thursday’s NATO summit in Brussels.
President Biden on Thursday warned of global food shortages as a result of the Russian invasion of Ukraine
Another example would be the article by Radio France Internationale titled "Poor countries to be hit hardest as Ukraine war threatens global food crisis".
What they don't tell is that Winter in Ukraine just ended and for the moment they did not produce any food as usual. The climate in Ukraine is considered temperate, but it is exposed to the Siberian winds and in Winter fields are covered in snow. How is it possible to face now shortages of food that is expected to be delivered at the beginning of next Autumn? Is it really a food crisis or a preparation for the next food speculation?
Update: @philipp answer and other comments state that the Russians products will not be on the market due to sanctions. But they will probably shift to Asian and African countries, the overall food supply will not be changed by the sanctions.