To initialize it just means to give it an initial value. It needs to be initialized as it would be undefined otherwise and you can’t work with it. If you initialize it inside the for loop it would be initialized each time the loop runs.
If you’re talking about these paranthesis (let i = 0; i < myArr.length; i++)
then no. Nothing else gets initialized there other than the i which is your number of iterations that the for loop does.