"Fruit" by itself is an uncountable noun. When we say "fruits" we mean "different kinds of fruit".

'Fruit' could be both a countable or uncountable noun. It is usually uncountable when we speak of “fruit” in a non-specific way as in your example. When you say 'would you like some fruit?' you are using here the uncountable noun 'fruit' with the plural 'fruit' as well. When emphasising the different kinds of fruits, we usually use the countable noun, e.g. in the sentence: " Fruits are good source of fiber , vitamins and minerals." Here you are using the countable noun 'fruit' and its plural 'fruits'. There is another meaning of 'fruit' besides the edible type of food that grows on trees (fruit vs vegetable). The word refers also to the part of a tree or a plant that contains its seeds. In that sense it is only a countable noun with the plural 'fruits'. 'A shub with small red fruits.'

thanks everyone)))