I googled as well. Ukraine exports were ~ 20 million tonnes. The tweet says the expected shortfall is ~ 7 million tonnes, probably because Ukraine is not expect

I googled as well. Ukraine exports were ~ 20 million tonnes. The tweet says the expected shortfall is ~ 7 million tonnes, probably because Ukraine is not expected to lose all of their production. If they did lose all 20 million, then the fraction would be 20 million / 778 million = 2.6%. Total production (including that consumed locally) is about 25 million, so if all of that were lost, the overall difference would be about 3.2%.