Apples are my favorite fruit.

My favourite fruit is the apple. Apples are my favourite fruit. The apple is my favourite fruit.

Keep in mind if you really like a fruit, typically you don eat just one. That might help you remember to make it plural. (I.e. I like cherries/ Cherries are my favorite fruit) Same can be said for many other things. (My son likes cars. My friend likes planes. My Friends like cruises.)

My favourite fruit is the apple. Apples are my favourite fruit. The apple is my favourite fruit.

The apple is my favourite food. or Apples are my favourite fruit. or My favourite fruit is the apple.